it depends what you choose to do with the angled walls.... wall or ceiling color? you wouldnt want navy over your head on the angles i think.

I suggest you keep ceilings and furniture white and add punch of color in lower accent walls, behind shelves or accented features / carpets / toys.

This room needs some decorator magic to protect that split AC unit and lock up the attic access door. You could try an indoor "Secret Garden" as the kids play space theme. Use white lattice over spring leaf green walls set out from wall about 2-3 inches. 4 ft Lattice panels would conceal that attic access door and cover the split AC. Think child safety so add hinges and concealed latches so only adults can gain access. Electric wall outlets are still accessible.

Hardwood floors with artificial grass area rugs. I'd play there - wouldn't you?