I like to try games without reading the description first, but I am not a clever man—at first I thought that the "[color] -> [color]" at the top was telling me which color destroyed what. I did figure it out, but I had to keep scrolling back down to see the color associations.
I really like the spell changing on movement mechanic, makes movement itself a more strategic element than it otherwise might.
I did notice that things would sometimes spawn off-grid, which made some levels easier and some more difficult, and the text doesn't stick to a 64x64 resolution, but otherwise, nice entry!