You guys when did the conversation about the new super civ end?
Let's pull it back.
Venice fits with purple. The doge of Venice was followed by people carrying purple flags, I do believe, and it's not hard to imagine how they could be...just totally different. At their height, Venice was basically the money of Europe, a more-than-decent military force, and a massive amount of culture.
The question would be how to make them totally different without 20 lines for their UA.
However, it fits the color and the alphabet.
However, more than the civ, I think the bigger interest is what makes it different.
Going about it civ first is logical, but only if you can figure out the civ.
What would make the Rooftrellen civ an entirely separate hypercube? You know nothing about the people, the history, the strengths...but you must have ideas about what could make them different.
Also, likely, it's a small change that will drastically change HOW you play the civ, rather than a huge change to the civ itself.