This is a fun little game and a pretty good concept. I like how the mood change was like a constant rhythm, maybe the music could go along with this rhythm? 

Okay. Like all other entries ... Why you a dedicated key for jumping and not the up arrow?!?! This is a major complaint of mine :D.

Anyway nice idea but an indication that you will change character would be nice. I fell of the level a million times thinking the flower had something to do with me changing colors.

Like the idea and graphics are really cool. I couldn't understand the bar at the top and got stuck inside blocks a lot. 

Lovely little game and nice concept. The sound fits the mood perfectly. As your character turns happy to sad perhaps add a different music track for unhappy vs happy. I like the checkpoints as I died A LOT. I did get stuck in the blocks from time to time, perhaps add a mechanic that pushed the player up to the top of the block if it reappears when the player is in the way. 

I prefer to use WASD to move which made controlling the character more difficult.
Overall I enjoyed it, I played it through a few times but I couldn't reach the end of the level.