I found Color Zen on the Zen Apps channel by Playboard curator App Junkie. It's a good pick for the channel: There are no points, no ticking clocks, and no stress. Just you, and a bunch of colored polygons to make sense of. As minimal as can be, but kinetic and beautiful, too.
The video explains it best, really. Each level of Color Zen presents you with a layout of flat, multicolored shapes. Drag a shape to collide with another shape that has the same outer color, and their outer color expands to fill the screen. If there are any other shapes with the same outer color, that outer layer is swallowed, and the next inner layer is exposed. You finish the level by eliminating all shapes, filling the screen with the same color as its border. Good thing there's a video to explain all that, right?
Color Zen keeps things simple, with a stripped-down, flat aesthetic. The shapes are basic, but some levels are intricately designed, with multiple nested shapes and thoughtful layouts. As you start moving shapes around, the levels lose their ordered layout and sometimes turn quite chaotic -- especially if you make any mistakes. Fortunately, it's easy to start the level over (there is no Undo, though).
Shapes do have inertia, and they can collide and bump against each other, so it's sometimes fun to fling a shape at the other edge of the screen and just see what happens. That's one way Color Zen is nice: You can use it as a simple toy, rather than a game with a goal.
Color Zen has an electronica-inspired soundscape, with mellow background music, and dings that sound off as the different colors collide and the colors spread across the screen.
Color Zen has no language, no cute characters, no leaderboards, and absolutely zero pressure. It's a great game for grown-ups, but it's very kid-friendly as well. A great take on ambient mobile gaming.