Paint thickness on cars shows how much paint is on any given car. Many auto paint companies are known for simply painting over a car's colour with another colour instead of pulling the paint off, applying car primer and repainting the car. As for the question whether paint primer can be put on top of the car's basic colour, the answer all depends on aesthetic tastes.
Different types of primer for a car are available. The high-build primer is very thick and will be the best at creating a coat to hide the original paint. However, having glossed paint that hasn't been sanded will make it harder for any of the primers to stick well to the car. Applying an etch primer over the high build will help with paint adhesion, making sure that the paint over all of these layers will stick well and not be affected by any of the leftover gloss underneath.
To get the primer to stick over paint could take up to four or five layers before being able to fully stick and cover up the under paint. Taking even a light wet sander over the original paint will help with the High-Build primer process. The last type of primer, known as wash etch, will not help in this situation as it is for bare metal and repairs, which this situation has neither.
While this is not the best method when it comes to a complete repaint of a car, it can be done to help save a small bit of time and repaint a car without the need for the extra process of stripping down the car's original paint.