The rule of thumb for this sort of thing is to never rely on color alone to convey important information. Shapes and patterns and textures are much preferable to simple color variations.

Thanks, looks much better. Ideally we could choose the two colors from a set of four or five colors.

Another option would be to use different forms, e.g. a round stone combined with a square one.

Anyway, nice game!

Looks like you've reverted the changes at some point today. Which is a definite productity win for me!

I also had this experience, thank you for fixing it so quickly. The game is fun!