I'm really glad you took the time to play our puzzle game! Thank you for the compliments :)
We'll definitely be making that more clear in the future with a more comprehensive tutorial (and some much simpler tutorial levels to introduce the ideas better) I'm also considering making a slightly transparent red plane over the hole, to help hint towards "maybe only red can get past the hole?"
If you or anyone else has any suggestions outside of a tutorial that you think might help make the hole dilemma more clear, I'd be happy to take notes!