RGB's original purpose was to paint parts of the world into being for the Celestial Bureaucracy, not too dissimilar from a certain white wolf from a fan favorite game. He uses the three colors we originally used for digital color because he was a (primarily) digital artist prior to his "induction" into the Bureaucracy, so they figured those are the tools he would be most comfortable using.

Given his outfit this is likely post-escape, perhaps restoring some glory to a park that had been left to wither or similar.

Art by the lovely  cbh