This app was mentioned in 13 comments, with an average of 1.23 upvotes
You might enjoy Color Zen for this.
Although whether any phone game is a good idea for sleeping is probably open to question! :-)
Some good ones already mentioned, I'll add Color Zen and Memento Bay
One of my favs. The IAP consists of new puzzles and extra tries which in fact you can earn the extra tries by watching ads.
https://www.youtube.com/watch?v=vQzPbezKOD0
The IAP is to unlock the rest of the game. No consumables. https://www.youtube.com/watch?v=IzPTwoGsxg8
This is probably the most beautiful puzzle game i've ever played. It's just a treat to watch playing. The way the paper moves and the colors interact it's just a treat
https://www.youtube.com/watch?v=KOrTRub2FYQ
Lyne is more focused on relaxing while Linken is more...intense I guess. Lyne definitely relaxes you with it's atmosphere while Linken has a more of a intense feeling from the get go.
Both are good but I prefer Lyne https://www.youtube.com/watch?v=MDQudjTzoLw
Thoughts:
If you are going to have 3d-look buttons, pay attention to the light source. The highlight and the shadow should all look like they are being cast from the same place. The exception would be if the button is meant to look pressed, in which case you can flip the shadow and highlight.
Fonts: general rule of thumb is keep different fonts to a minimum. One serif and one sans serif font would be an example, or one sans serif font in bold for headings and regular for body text. Script fonts should be used very sparingly and only in contexts that make sense, like a wedding invitation. Don't have two different sans serif or two different serif fonts on the same page.
As others have said, it's easier to pull off a flat look. Check out Color Zen, Shades and Bicolor to see this done well.
I second the suggestion to use Kuler. Or even a simple look at a color wheel and use complementary colors.
I am a designer, although I haven't done much with UI. Feel free to pm me if you need any help.
Color Zen - 4.1 rating - Free with IAP - Search manually
Zen Squares - Minimalist Puzzle Game - 4.6 rating - Free with IAP - Search manually
Tangram Zen - 4.2 rating - Free - Search manually
Zenge - 4.3 rating - Free - Search manually
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could be Color zen
was in a Humble Bundle or App All Knight from a while back, not sure which.
I'd add Color Zen to that, lovely soothing game, but addictive. Great music too.
Top Free
Socioball
Color Zen
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Osmos HD - relaxing combination of graphics and music, almost meditative
Monument Valley - beautiful art
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Top Gems
Bounce Out - fun, unique puzzle game
Mr. Jelly - simple platformer, good graphics and music
Get 9 - challenging math puzzle
I'd recommend Color Zen for this type of game, they basically copied it.
https://play.google.com/store/apps/details?id=com.largeanimal.colorzen