Nice game. the visuals are very neat and clean.
The gameplay is oddly satisfying and addictive. I found myself clicking on retry instantly after I lost just too try and do better.
It took me a while to understand how and when to merge (not sure i fully got it thought) but it might be just me. ^^
I had the same reflection as the comments bellow while playing : "why cant I see what color I'm shooting ?" but I understand it's on purpose.
All in all, very good game ! good job :)