Just something I noticed which I’m not sure if it’s a bug or not. If you don’t specify a colour in your car design you get random ones, however these still include the colours that you have to unlock - I’d have thought that you should only get basic colours if this was the case. You’ll see below that I’ve got purple, peach and regency red in there despite not unlocking them yet.
Haha, thats definitely a bug 
(I’ll fix it :D)