The concept is promising. But I also had issues understanding how to change colors.
The other problem I encountered is that... I'm colorblind. :p So, yeah, that brings obviously some difficulties. The colors that were hader for me to differenciate were 5/6, and 2/3. Surprinsingly 1/4 wasn't too much a problem, though it is still a bit tricky when they're far away. However, I think there might be solutions to make the game more accessible.
With a bit of concentration, I was able to recognize 2, 3, 4 and 1. But what made it difficult was the thinness of the cells. Colorblindness works a bit like myopia (at least for me): the more little a thing is, the harder it is for me to peceive its color. I thus had to look my screen closer and squint to see if a cell is blue or violet, while I had no problems with the numbers in the UI. So I would suggest a way to have larger cells. While it might break the aesthetic, it could help a lot.
My second issue was the glowing effect for the tile where the player stands. It can really makes them hard to read. Orange fading to white makes it look like yellow, and it doesn't give enough time to focus on it. So I had to move to see its actual color, and, well, that just create other problems!^^ So again, as nice as it looks, I would have liked to be able to disable this effect.
Otherwise the concept seem really cool. And the minimalist visuals are pleasant, giving a really clean UI! So I hope this perspective on colorblindness issues can help.