Om anything Repeating command block with always active 1. U build a sphere of whatever block u need. A half sphere) Then do on the command block /execute @e[type=snowball] ~~~ execute Splotchycello24 ~~~ clone (the the half circle thing's coords) ~~~ masked
Or do this for painting with the command block /execute @e[type=egg] ~~~ setblock ~ (y coords) ~ (s♥♥♥ all block u want)