@Nefliqus
PreGame was made to change the settings before the game start and at this time player:GetColor is not possible.
Now, if you want the favorite color of a civ, then you need to look at the XML data (GameInfo.PlayerColors ?). But the game may actually use a different color choice if there was some conflict between two civs.
Also, be careful: some colors are strings that related to the RGBA values defined in XML while others are tables with four fieds (r, g, b, a).