The object is to start at one of the black squares and get to the other one. The path must cross through all of the cells. That's the suggested route. You could start at any cell. Just find a path that crosses each and every cell.
Each cell has an inner square color and an outer color. One of the 2 colors must match either color of a neighboring cell in order for them to form a path.
24 Easy Levels
24 Medium Levels
24 Hard Levels
I did all the Easy & Medium levels and maybe 5 of the Hard ones. I like this concept. The only problem I have with it is the actual colors. It's an explosion. I've actually solved many of the levels without really paying attention to the colors because drawing a path through every cell - there aren't that many possibilities.