Use the options-menu to make the AI use your setup and skin. Then choose the desired skin/setup you want the AI to have. Then click "Add AI" as often as you want. Then change your skin/setup to the combination you want for yourself.
You can also name colour setups (colours & skin) as 'AI 1' to 'AI 12', then when you add an AI they will use the skin of their name. You can therefore have an AI grid full of skinned cars.