Great game
A few comments though:
1. You should be able to tell the difference between solved and unsolved levels. The little difference that exists now is simply not enough.
2. The drawings are very bad. I saw another picross game that did a MUCH better job drawing in every single format, from 5X5 to 15X15, and some of the ones I saw here were simply horrible. So I advise you to get better on that.
3. Highlighting the colomn and row you're pointing on might be very helpful. I don't know about other people, but on bigger puzzles like 20X20 I often have trouble recognizing the row and colomn i'm working on.
Other than that, great flowing gameplay, definitely a picross game i'd recommend to other people.