Thanks for the feedback!
Yeah.. we should have provided more feedbacks to players about various events going on in the game. Sadly, we didn't have the time for that.
For your question, a sample greys out when it's condition is not satisfied so it will not be played. New samples placed onto the track will be disabled for the current loop if it is already playing. Since we didn't provide enough information, we simplified the game in a way where arbitrary decision won't result in bad things and the music usually remains good.