Color Stock Bonus is a game mechanic that rewards nations for being on the same color as their Alliance.
A nation that matches their alliance's designated color will receive a 3% gross income bonus. This does not apply to Beige nations, who will receive a 5% bonus regardless of whether they're in an alliance or not.
Nations on the color Gray do not receive any Color Stock Bonus.
The color Beige always has a 5% Color Stock Bonus, regardless of treasures. Alliances cannot choose Beige as their color.