inside each skins, you can customize colors in its file skin.ini
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Note: the driver type (modern or vitnage etc.) is set inside the data of the car, so the model itself you can't change without affecting the data of the car.
and what colors are available depends on the type, here "sparco_racecars_Tide_RG9" glove, or "plain" suit etc.
if you're familiar with folder structure in windows, you can find all the color combination here :
So for example for the SUIT, you have choice between classic/ or plain/ etc. and inside their subfolder, they each have their own choice of colors
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hope that makes sense