It is a fantastic gamplay. Do you actually have these "50+ levels"?

Maybe, you should even stay without colors.
Remove the colors of the cow, as well, maybe let remain a touch of red in the cloak.
put grey to white fantasy landscapes in the background.
Limbo-alike - or do the opposite like in Braid full of bright changing colors...

Just some ideas.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt