Mathematically speaking, there are ~20 colors that the game currently utilizes to distinguish civs from one another. One (black) is reserved for city-states when used as a background, and two others (navy blue and dark teal) are somewhat hard to distinguish from one another if they share the same icon color. This leaves 19 color options for the icon, and 18 for the background, for a grand total of 342 possible combinations. Well, 341 once you discount barbarians. At a rate of 1 alt leader for every 8 civs, that also meant about 30 new alt leaders, leaving 311 new civs (it ended up being 309 new civs with 32 new alt leaders). So of course I thought, "309 civs? I've seen far more ideas than that on this forum, we could easily fill out this set with room to spare!" And then sought to start filling it out, with icons. Full-blown abilities and the like would have even more insanity than this was. Civs that already have a popular mod for them just have the name of the mod creator in place of the icon so as to not re-invent the wheel, but I also didn't want to use the icons without permission either. Feel free to check out the mods if you want to see those specific icons. Spoiler Icon Table : Things I've learned from this: 1. I was wrong, 309 is far too many. I hit the point of "I would be content if these were all the civs to ever be included in the franchise" somewhere a little after #100, thought I started grasping for straws at around ~#175, and really started grasping for straws around ~#250. I started creating lists of potential "if I run out of ideas civs" as I did my research, then ended up exhausting all of those as well and then some. 2. With that said, there were far more than 350 polities that could make interesting civs. The bigger issue was where to draw the line between polities that morphed into or were conquered by another, especially when from a modern viewpoint they're viewed in continuity. Things get even more complicated when you consider states of semi-independence, like vassals that were left to their own devices or intra-polities that retained autonomy for centuries but were never independent. A lot of the polities I ended up splitting into their own civs versus keeping as a cohesive, era-spanning one ended up being nearly arbitrary. 3. As a corollary to the above, the civs that had priority for alternate leaders were 1) vanilla civs, and 2) civs that represented either long periods of time or multiple different polities that were not split into their own civs. So the Mongols didn't get two leaders since many other khanates get their own representation, but Siam does because Ayutthaya and modern-era Siam are not given their own civs. It's not perfect, but with the allocated 30ish alt leader spots I tried to give each civ only 2 leaders at most. 4. Technically speaking there are hundreds of people groups and indigenous tribes that were left out. However, there's only so much you can do to distinguish dozens of hunter-gatherer cultures from each other with 4 uniques per civ. I elected to give each region of North America at least one if not two NA groups, even splitting some regions into subregions (Alaska, Pacific NA, coastal CA, inland CA, Southwest, Baja, etc...), each region of Australia an Aborigine group, and other continents representation of either their largest or most well-known groups. 5. As for modern nations, most regions have a modern representative, but similar to the last point there is only so much you can do gamewise to distinguish them. I tried to choose options that were either popular in mods, had something that might be interesting about them mechanically, or would cover a bit of the map that for whatever reason had no civ representing it. As a side note, if you were to color in a map with territorial ranges of each civ, there would be virtually no empty spots save for Antarctica, and even then that would be filled if you considered modern claims. 6. Many color combinations are, to be frank, quite ugly. There's nothing that can be done about this fact, though, as by the constraints of the proposal there must be a civ for every color combination, regardless of clashing. Additionally, some color combos are very harsh on the eyes or illegible in their usual tone and required either lightening or darkening in order to alleviate this while still staying in the range of their name. 7. Also color related, it is frankly impossible for every civ to have an ideal color combination in the absence of a jersey system. Of course this is a problem Firaxis has noted as the very reason the system was necessary, but it became painfully clear throughout this process. Once the reds/blues/yellows/whites/ started filling up, I started settling for maroon or pink for red; tan or brown for yellow; purple or teal for blue. Then those started running out of room, and around icon ~200 the color choices became near-meaningless. They tried to stay somewhat faithful if possible, but honestly no culture in their right mind would want Purple/Orange-Brown as their national colors unless its capital was Halloweentown (sorry, Palmyra). 8. In keeping with the Civ VI design philosophy the icons are as simple as possible, with a leaning towards plant and animal motifs. To keep things distinct I tried to keep lions, dragons, and eagles to a minimum (ie: for Austria I went for the edelweiss instead). For a specific outlier, the dragon was far too iconic for Bhutan, but I was unable to simplify it for the icon; if it were to appear in Civ VI as a city-state or the like, I'd expect a still-full-bodied, but stylized version; I just don't have the skill to draw it that way. You could squeeze in maybe ~25 more civs/leaders if you separate navy blue from regular blue and utilize the combos with black that the CS's don't already use, and maybe a few more by separating the hues of gray (though the light grays are hard to read with the light colors, and the same for the dark grays and dark colors). But honestly there isn't much to represent other than, as I said before, various indigenous groupings and ancient cultures. Spoiler Icon Origins : Red Switzerland: Not mine Denmark: From the Vikings scenario Soviet Union: Flag Spain: NA Moldavia: Coat of arms Albania: Coat of arms Mexico: From Mexico City CS Moor: From the Black Plague scenario Nepal: Flag Korea: NA Maori: NA Indonesia: NA Morocco (Alt): Flag Spain (Alt): NA England: NA Yugoslavia: Coat of arms Murri: From the Outback Tycoon scenario (New South Wales, it's a kookaburra) Barbarians: NA Maroon Mongolia: NA Armenia: Not mine Chola: From the Nirvana scenario Colombia: Condor Normandy: Not mine Mali: NA Portugal: Rooster Morocco: Flag Ragusa: Coat of arms Greece (Alt): NA America (Alt): NA Acadia: Flag of Acadiana Hawaii (Alt): Hibiscus Burgundy: From the Yonne coat of arms Malta: Coat Goth: From a gothic brooch Portugal (Alt): Rooster Hun: Civ V Pink Genoa: Genoa lighthouse Haida: Salmon/whale France (Alt): NA Navarre: Coat of arms Aram: Modern flag Latin: Coat of arms Amis: Bamboo Tatar: Modern flag Faroe: Ram Sicily: Wheat triskelion Powhatan: Squash/pumpkin Comanche: Modern flag Hawaii: Hibiscus Byzantium (Alt): Labarum England (Alt): NA Poland: NA Etruria: Pendant motif Beothuk: Iron tool design Tan Wales: From Cardiff CS Scythia: NA Poland (Alt): NA Tongva: Mission bell Navajo: Modern flag Karenni: Modern flag Yaqui: Flag Rwanda: Coat of arms Bosnia: Coat of arms Wabanaki: Dreamcatcher Talamanca: Toucan Assam: Figurine Sassanid: Not mine Minoa: Motif from 'Prince of Lilies' Deseret: Beehive Philistine: Fly Nubia: NA Iroquois: Four Direction symbol Gold Kongo: NA Pueblo: Zia Kongo (Alt): NA Siam: Not mine Serbia: Double-headed eagle Brunei: National emblem Jamaica: Pineapple Brazil (Alt): NA South Africa: Coat of arms Xiongnu: 'Stag with eaglehead' figurine Kievan Rus: National emblem China (Alt): NA Muisca: Parrot Khotan: Silk butterfly Laos: White parasol Russia (Alt): NA Nubia (Alt): NA Russia: NA Orange Anangu: Uluru Songhai: Not mine Bahrain: Flag Kyrgyz: Flag Sri Lanka: Flag Bhutan: Flag Ireland: From Armagh CS Cherokee: Modern flag Netherlands: NA Miskito: Coat of arms Netherlands (Alt): NA Madagascar: Merina Kingdom flag Maratha: Figurine Pala: From the Nirvana scenario Aragon: Coat of arms Novgorod: Stag Noongar: Snake design Belgium: From Brussels CS Copper Canton: Flag of Guangzhou Italy: Not mine Pontus: Unknown, from Total War Siam (Alt): Not mine Cornwall: From Duke of Cornwall flag, simplified Sikh: From religious symbol Arabia: NA Chumash: From Chumash rock art Khmer: NA Uzbek: Cotton Funj: Branding mark Phyrgia: Phyrgian art Champa: Plumeria Muscogee: Eye-in-hand symbol Arevaci: Relic Sao: Simplification of horse-riding figure Hyksos: Art motif Dene: Bear paw Light Green Mossi: Mossi antelope mask Numidia/Berber: Not mine Tunis: Tunis Coat of arms Zulu: NA Brazil: NA Oman: From Muscat CS Zapotec: Relic Tarascan: Glyph Tupi: Feather Sami: Sami sun symbol Azerbaijan: National emblem Lesotho: Flag Guanche: Figurine Burundi: Flag Lombard: Flag Haiti: Coat of arms Caral: Caral site pattern Zimbabwe: Zimbabwe bird Dark Green Hungary: NA Yucatan: Yucca Lithuania: Horse from coat of arms Benin: Leopard mask Australia: NA Ethiopia: Not mine Arabia (Alt): NA Hausa: Hausa people emblem Livonia: From the Poland scenario Chuvash: Flag Iceni: Triskelion Olmec: Olmec head Nakh: Nakh carpet pattern New Zealand: Kiwi China: NA Abkhazia: Flag Caddo: Modern flag Larrakia: Modern flag Blue Norway: NA Castile: From the Black Death scenario Iceland: Not mine France: NA Philippines (Alt): Not mine Sumeria: NA Montenegro: Coat of arms Burma: Not mine Cree: NA Mapuche: NA Ghaznavid: From the Nirvana Scenario Greenland: Coat of arms Iga: Shuriken Kimberley: Baobab America: NA Khazar: Proposed modern flag Cuba: Phyrgian cap on coat of arms Prussia: Eagle Light Blue Chile: Flag Ainu: Flag Japan (Alt): NA Argentina: From Buenos Aires CS Sweden: NA Boer: Wagon Tuva: Kyzyl flag, simplified Burma (Alt): NA Nicaragua: Flag Sweden (Alt): NA Ajuran: Gazelle horns Mari: Mari lion Harappa: Harappa script Seulucid: Not mine Greece: NA Finland: Coat of arms Modoc: Wapato leaf Amalfi: Amalfi lemon Teal Kazakh: Kazakhstan flag Aztec: NA Panama: Coat of arms Yupik: Yupik mask Philippines: NA Ethiopia (Alt): NA Galicia: Modern flag Samoa: Crux Yakut: Proposed modern flag Rapa Nui: From Rapa Nui CS Metis: Canadian Metis flag Kalinago: Seashell Taino: Not mine India (Alt): NA Mercia: White wyvern Sibir: Siberian Tatar flag Calusa: Alligator Tlingit: Totem head Dark Teal Moravia: Coat of arms Vietnam: Chim Lac Swahili: Not mine Egypt: NA Gaul: Not mine Arakan: Rakhine state seal Akkad: Not mine Maya (Alt): From Palenque CS Maya: From Palenque CS Vietnam (Alt): Chim Lac Pandya: Two fish symbol Babylon: From Babylon CS Mughal: Ashoka chakra Egypt (Alt): NA Taiwan: Flag Bavaria: Coat of arms Cucuteni: Art motif Oyo: Yoruba Opon Ifa board Magenta Persia: NA Sardinia: Coat of arms Persia (Alt): NA Guarani: Modern flag Buganda: Coat of arms Tahiti: French Polynesia flag Cuman: Coat of arms Kenya: Flag Costa Rica: Tree frog Parthia: Assur temple art Hiva: Hiva mask Tonga: Tonga headwear Fuegian: Sea lion Byzantium: Labarum Angola: Angola sun Kunin: From Outback scenario (wombat) Bactria: From Hephthalite tamga Chimu: Fabric pattern Purple: Frisia: Flag Korea (Alt): NA Kuninda: Triratna, on coins Khitan: Pagoda of Tianning Temple Rome: NA Jimma: Oromo flag Saba: Sabaean inscription Nri: Palm frond Rome (Alt): NA Sulu: Flag, simplified Phoenicia: NA India: NA Iroquois (Alt): Modern flag Malaysia: Not mine Iroquois: Modern flag Mycenae: Mycenaean octopus Palmyra: Gazelle Ryuku: National emblem White Canada: NA Japan: NA Genoa: Coat of arms Austria: Edelweiss Papal States: Coat of arms Georgia: NA Luba: Figurine Saudi: Flag Ottoman: NA Scotland: NA Seleucid: Not mine Inuit: Inuksuk Texas: Bull with lone star Venice: Venetian lion Assyria: Not mine Brittany: Flag California: Bear Botswana: Zebra Gray Bulgaria: From Preslav CS Timurid: Flag Romania: Eagle Manchuria: Imperial Seal Bohemia: Coat of arms (lion tails) Manx: Coat of arms Ottoman (Alt): NA Afghanistan: From Kabul CS Israel: Star of David Uyghur: Emblem, simplified Dakehl: Beaver Tibet: Not mine Frank: From Black Plague scenario Vandal: Unknown, from Total War Pirate: Jolly Roger Elam: Dove relic German: NA Brown Ashanti: From Kumasi CS Nabatea: From design on tomb Palawa: Tasmanian devil Epirus: Unknown, from Total War Inca: NA Northumbria: Coat of arms Hittite: From Hattusa CS Toltec: Modern flag Bornu: Kanem flag Tehuelche: Modern flag Illyria: Flag Shoshone: Civ V Lydia: Coin face Punt: Proposed hut design Mississippi: From Cahokia CS Inca (Alt): NA Germany (Alt): NA Blackfoot: Buffalo Conclusion: In terms of visual clarity the game can support over 300 distinct civs. For the sake of quality, it really shouldn't get anywhere near that.