Also, some cars won't have it listed (like the race cars, concept cars and even some production cars). But it should be around the top left corner when you're viewing a car.
GT Auto doesn't let you see what paint chip a car currently has. However selecting on a car from the Garage should give you the name of it at the top, above the car previewer. It also has a small square next to it that has the paint chip's hue preview.
