Question regarding primer thickness

I was just spraypainting my model with primer, I was wondering how thick the primer has to be? Does it have to be thick enough to not see the original color of the model?

Thats what ive heard. Also, make sure you don't spray too much and lose detail ex: panel lines etc.

Color coverage is very important especially when doing lighter colors sucha s white,orange,yellow an red. An example if you are painting a car red over red plastic you need a a good solid white base, if you have any bare red plastic showing the red will be dark in those areas.