This felt like well done puzzle game, good job! For me, the game might feel easier if instead of numbers, there'd be just different shades, for example you'd need to blend a darker area of the field (currently 2s and 3s) with a stack of multiple clouds to achieve the desired lightness (or currently the "0" state). Then again, the current implementation is perfectly fine as it is, and nicely technical, too :--)
Also, the fact that it actually rains after completing the level is just perfect, feels really nice. I would have liked to see that cute smiley cloud too after finishing levels!