At first I only had the indicator on the colour wheel, that was really hard.
Then I tried to just switch the background's colour but that was flashing way too much.
So I settled with that backdrop "poster".
The trick is to anticipate which colour is the active one on the next field and then see if it comes up in time... which is (one of) the reason(s) why they don't just pop up in the front of the stones but are set into the sphere that rotates on each move.