Starting in the 90's all chassis' are grey as stated, before that it was kind of up to them, examples- Dale Earnhardts Wrangler car had a blue interior and Mark Martins Folgers car had a white interior. It will probably tell you right in the directions the color they used but definitely search for info and pics on line. The chassis' are close but you will find little differences between the manufacturers mostly in the engine but I have noticed the floor on the Monte Carlo and the Grand Prix are a little different where the seat sits. As for trading I learned also unless you have odd kits there is not much want for them, I did learn however (I noticed you have 2 of the same kits) you can get decals from somewhere like Mikes and make them 2 different drivers cars or even a car they never made a kit for. I just recently did Rusty's 1989 Kodiak car that way.