A very relaxing game mechanic, I loved it, although I didn't understand, why the levels suddenly jumped from 8 to 41 in Solar Panel stage! And sometimes I got a bit frustrated as it felt hard to understand the rules in level 3, though it may be just me so is not a problem! And I found a bug, when i complete level 41 from Solar Panel stage, and click Next, it sends me level 2!
By the way, the UI is very much polished! Good job!
Anyways, nice concept, all the best improving it!