The purpose of a vehicle colors chart is to index the exact color used to paint vehicles of specific makes and models. Different manufacturers use different colors of paint, and these colors can even vary slightly from year to year.
The chart helps to match exactly the same color originally painted on the car. When a car needs a paint touch up to fix a scratch, or the car receives a replacement part like a door or a bumper, the painter knows the specific color to match based on the car's manufacturer, the year the car was made, and its model. Some websites like AutoColorLibrary.com will even match a paint dating back to WWI for historical accuracy.