Why do people paint their cars with flat black paint?

It's primer paint . It's used as a base coat for a paint job . It keeps the metal from rusting,etc while they get all the rough spots out of the car body . If someone has a car with a red finder, blue doors and a white hood they may go ahead and primer the whole car just to look better .

It's trendy to "murder out" your car.

It's just another type of paint job.

People are also now painting their cars in matte colors....blarg.

They think it's cool like a batmobile.

Saw one done to an Aston Martin DB9. Didn't think that was cool..... Hard to maintenance also.