wow. when i read the op, i couldn't believe anyone would think those colors were dark - and then i was totally surprised by the other posts. op, i'm a big fan of multicolored rooms. in our old house, ds1 had a little 8x11 room with slanty ceilings (a dormer). we painted the walls and ceiling a really vibrant yellow, trim around the window and doors sky blue, the wood on the window itself and the doors orange (like, candy corn orange) and the baseboards a true blue (similar to painter's tape, or kind of crayon blue?). everyone thought we were completely insane. IT.WAS.AWESOME. and when it was done, everyone loved it. this was a nursery for an unknown gender baby - the other details were a wood floor with a multi-stipe rug (ikea strib if you want to see) and natural wood furniture. it seriously kicked a**.
new house - the finished attic is the kids' room. we haven't painted up there yet because we need to wait until the weather is warm enough to have the windows open, but we are planning to paint the vertical walls (which are about 4.5 feet high) all different colors. we'll keep the slanted walls and ceiling white, with white trim. their furniture is white as well. the room is very similar to your play room.
i think you will have no problem combining these two colors. i would suggest doing the low side walls, slanted walls and ceiling in one color, and the two end walls (window/door walls) in the other color. i think that would look great. i love the colors together.
but . . . the main floor of my house is three shades of blue, two shades of yellow, and purple, so what do i know?