First, try to remove large groups of blocks that are not the colors you need for the butterflies
This should build up the paint brush booster quickly
Use the paint to change some blocks to the color you need to release one of the butterflies.
Next, use a balloon to clear some, more balloons will fall
The trick with this level is finding a balance of when to use the balloons (so more blocks fall) or when to wait.
Saving the correct color blocks until almost all of the 16 you need to release the butterfly is a more efficient way of playing.
But this can also mean less blocks fall so it's harder to get enough
Keep count of how many of the correct color blocks you have as you play.
When you get to almost 16 use the balloon/s to remove them and hope more will fall!