For the normally available colors on the Carrera GT, my favorite was Seal Grey. I don't know how many custom colors they had available for an additional price (like on the regular models). I know that Seal Grey is the normal dark grey color they offer while an example of a special order one is Slate Grey.

The normally available colors on the Carrera GT according to the website are Black, Guards Red, Fayence Yellow (solids), Basalt Black, Seal Grey, and GT Silver (metallics).