I like the idea, but as others have said, the puzzles were too easy. Sokoban is known for very difficult puzzles which often require planning and exact movements of the boxes. An idea you could try out to help improve the level design, is take some sokoban levels (either originals or other levels that people have made) and trial and error tweak them to use different combinations of your colors.
Congrats on your first title! As you said in your end credits, I hope this inspires you to keep experimenting and working on games :)