Mighty car mods myth-busted it and found that it runs 40 degrees colder than one that isn't sprayed (with and without airflow on average).
The science behind it is to do with objects radiation and black changes this property or somthing... Watch it on youtube!
I thought it could make a tiny before watching but 40+ degrees is just MENTAL from a can of paint and ech primer. Next cheap mod to do when I have time!!