Like this:
https://i.pinimg.com/564x/de/63/c2/d...c56f023672.jpg
It would be cool if you would have a sidequest for pictomancer to go and collect different paints. Like the sidequest for Bard to get the instruments. But a bit more exploration, maybe with some colours locked behind some content. This could be an interesting way to add more rewards to older content. For example: You start with the base RGB. And if you do POTD with a pictomancer to like floor 50 or 100, you could get a Jet black dye and add it as a colour. Or finishing a Raid series like Crystal Tower would give you another colour (Maybe cyan?). Just an idea, I think it would be fun and it would incentivise people to at least try some content, but not force them to master it.