Like how the fuck was Simon ungommaged in the abyss
Renoir was choosing to gommage Aline's oldest creations, which were the ones least protected by her power, likely because she was choosing not to protect them to conserve her strength.
He intentionally chose not to gommage Simon so he could attempt to take control of him. When you find Simon he's mind broken for Renoir's efforts, but avoiding doing his bidding through sheer will.
why the fuck did Clea's assistance make the chroma corrupted and unusable instead of just making it switch over to Renoir's side
She had to corrupt it, otherwise Aline would claim it instead of Renoir, being the stronger painter.