Great work, does what it says on the tin. Didn't encounter any bugs. Little bit more polish, sound, music and animations would be cool. But great work.

If this is your first-ever game, then you are off to a solid start.  I saw the source for your project and saw you built this in js from the ground up.  As a fellow 'from scratcher', I can say you know your stuff, you know how to put stuff on the screen and you have an understanding of game concepts.  I have seen much worse starts than yours, so take this as a sign of encouragement, please.  It looks like what you need to figure out how to make better use of variables for working game mechanics, such as basic enemy AI, but that's something that comes with time, practice, patience, practice, determination and practice.

... Did I mention practice?  I am not sure.

Neat concept and well executed!

Cool concept! I love how dynamic the coloring is, I'd have no idea how to make something like this!

Nice and simple sandbox. Is there any combination or sequence of colors that'll give me the rainbow color shown on the cover image? 

Fun! I always like a good alliteration too.

Nice job! I like these kind of “toy” games that are like little sandboxes. Not all games need an end goal–sometimes a cauldron laboratory for color mixing is all we need.