Awesome idea for a game! Plays really well. The committed jump arcs might not be to everybody's taste, but having grown up with platformers that use them I felt they fit really well. The color shifting idea for the gravity adds a nice spin. You adhered to the colors of the jam really well. And your font is pretty cute, as is your main character.
That being said, I would prefer a button to cycle through powers from left-to-right and vice versa. Have to reach for my mouse constantly really detracted from the flow. A pause menu with a color select could also work wonders. And while you don't need sound effects, a few subtle ones for the jump/gravity shift and some extra music would immensely add to the immersion. Also, if you move left of the first red block, you get softlocked.
All that aside, great fun. The physics are very tight and you did a great job coming up with puzzles. I could see it running on an old handheld.