You are absolutely right about the UI being hidden, and my plan is to have a shortcut key to directly change between the three main colours, for a faster swap and a clearer view of what appears/disappear on screen. It's also aready planned a change for the candles as I have received many feedback about them being very short timed, and to help the players even more I'll implement some kind of more specific hint for each puzzle.
I really appreciate you taking your time to give me your feedback and ideas for the candles, I'll think about it, anyways thank you :)