Well, i suppose i will give away the answer and declare open floor

It was just too difficult to guess, although i hope it might be seen as somewhat educational (?).
Black: Countries specifically mentioned as places where works by Kafka take place, either in their present time or at some time before the beginning:
-Belgium (there is a fragment about someone taking part in the Olympiad of Antwerp).
-Congo ("It was not a pleasant life i was living in Belgian Congo"). Existent in a fragment, not a full story.
-Germany (The main character in the novel Amerika begins his journey from Hamburg, althought the story starts when he is approaching New York- however the statue of liberty is altered, carrying a sword, so it might be a dream as well).
-US (in the novel Amerika).
-Russia (mentioned in many stories and parts of them take place there. For example in The Judgement -Das Urteil).
-Occupied Thrace

(large fragment, about someone on a business trip to Constantinople).
-Arabia (not saudi arabia in particular, but some desert land populated by arabs, it is the setting of the short story "Jackals and Arabs").
-Latvia (The story "Hunter Gracchus is taking place in Riga).
Green: Lands where works are either seemingly take place (but they are not specifically named) or lands mentioned in works but the works not taking place in them nor are any non-historical characters from there.
-Greece (Apart from a number of mythical-centered stories such as The Silence of the Sirens, or Poseidon, also in the very short piece about Alexander and his sword always pointing to India).
-India (in the above story about Alexander and the thoughts of the East).
-China (Well, i was tempted to place this in the Black category, but in reality
if i recall correctly the large story "On the building of the Great Wall" never once mentions China, despite being obviously about a huge wall to protect against northern barbarian tribes).
-France, Ireland, Romania, Germany (all have nationals being part of the novel Amerika. From Butterbaum, who steals the suitcase of the main character, to the two street-wise companions of his in later chapters of which one is french and the other is irish, and of course the coaling worker on board the ocean-liner in the first chapter, who is of Romanian nationality, and so is the ownership of the ship).
-Italy: The visitor that Joseph K. is supposed to meet again in the Cathedral is from Italy.
Red: Places where noted dreams of Kafka were placed.
-Poland (a dream about the yiddish theatre)
-Germany (various dreams, such as the one about his "Trial" by the relatives of his first fiancee).
-France (fragment of a dream centered in Paris).
-Montenegro (dream of a person wearing traditional montenegrin clothes, a native of Montenegro).
Purple: Places mentioned by Kafka in his notes, not linked to the actual travel notes.
-Greece (a mention of a Greek doctor in some train).
-US (at least one mention, of political debates and anecdotes from the election of FDR, "threatening a man by raising his plastic cup).
-England (apart from a couple of notes about Dickens, there is a short diary entry which refers to Sherlock Holmes and a kind of window-gazing).
-Spain (various bits about his uncle, who lived in Madrid).
-Turkey (
iirc this is mentioned in a dream, but i am not sure if it was Kafka's or another author from his circle and he just wrote it down. In the dream someone is cursing the author Franz Werfel as being a "turch". Kafka notes that this was a term of a local dialect, and a corruption of the term "turk", this was in Austria and Kafka argues the term was used in remebrance of the old Austrian-turkish wars).
-Austria (Kafka expressed in writing in his diary his aversion to immigrating to Vienna).
-Czechia (various notes about the local literary life, the one in the Czech language which Kafka spoke to a considerable degree).
-Poland (in the early parts of the diary, where he focuses on the Yiddish travelling actors).
-Russia (a lot of notes about Russia as a metaphor, due to its vast size. Also to some authors, mostly Dostoevsky and at least once Gogol. However i did not use the mere reference to writers as a reason by itself to utilise this color, otherwise there would also have been some other countries in purple, such as Norway--due to Knut Hamsun).
-Serbia (a note about the "stupid defeats in Serbia" written a short bit after they were happening during WWI).
-Persia (a small note about someone who claimed a sentence written by Kafka as part of a small poem, was "of persian rhythm").
*
That is all, i guess
