Verb: 1) to strike repeatedly, to pummel, to spank, to wallop.
2) to teach a lesson (or lesson of dominance) through physical abuse; demonstrating superior strength.
The term seems to have sprung from the late 60s to early 70s in Americana. It's a term you'd hear spoken by Red Foreman on That 70's Show, and by the older brother on Supernatural.
(brother-to-brother POV) "If you tell Mom I set the curtains on fire again, I will paint your ass!"
(mother-to-child POV) "You can touch those muffins...if you want me to paint your ass!"
There is no diminished meanings when used in any American culture or race.
(Mexican mother-to-daughter POV) "Oi Maria! I paint ju ass twice already, why you still date Oscar?"
In construction work an ass painting is used as an initiation type ritual or right of passage for one seeking to learn the trades.
1st yr apprentice: "I told my journeymanmy favorite color was red not knowing I was getting an ass painting... so needless to say i went around looking like a fuckin babboon for a week.
Alyssa: Damn, Asiana, why is your ass so red?
Asiana: oh, Asher went too hard on me yesterday. He fell in deep. Now I have Ass Pains
Alyssa: oh, I’m sorry! Bet it felt good though.