Thanks, for level 49: each time tap the last square that was added. Maybe you can draw on a piece of paper which ones you already clicked to make it a bit easier. Or another great help in the second half: concentrate on the black instead of the yellow.
If you really can't remember, the hints will show you which square to press.
@BartBonte
Thanks for your five stars!
If you enjoyed the game, maybe you can try one of my other color puzzle games, there are already 6: YELLOW, RED, BLACK, BLUE, GREEN and PINK, each with 50 new levels.
@BartBonte