Yes you have seen lots of NON alloy blocks painted, i.e. iron etc, which is fine!
NEVER paint an alloy block! Why do you think F1 engines have alloy blocks!
DON’T PAINT IT! Unless you don’t care, alloy is excellent at dispersing heat, painting it may look nice, but will trap the heat in!
Same reason you shouldn’t polish the surface, it is rough so as more dense to help cooling!