I know years ago you could change the tint of blocks but I have no idea what happened in the like 2 years since i played this game. I am backa and can only find ways to tint items or icons but not blocks.
Paintbrush is an easy craft if you don't find one. paint can be crafted in the chem station, but scrapping dyes is the easy way for me unless i need a ton of it.
AFAIK this can't be done right now. They did show some new blocks for a20 that were just tinted version of existing vanilla blocks. But I don't know if that means it will be possible with xml, or if they just made a bunch of variations of the textures.