Idea: "stack" white blocks.
You could "stack" white blocks on the same spot, to power up that attack.
So you have the option to spread out & do multiple attacks, or "stack" up the damage into a single HUGE ball of death (for example).
So, lets say you have 3 blocks, you can either spread them out (eg: yellow 1, 4, 7) or stack ALL 3 of the blocks (eg: on Yellow 1) and it does 3 times as much damage in 3 times as big area.