+ & - : A Zen game

Are you tired of the usual games where you just slide your finger across the screen at random to make a decent score ?
With +&- you'll have to use your head to do something good.
The rules are two:
1) equal numbers on background of equal color are added
2) different numbers on background of different color are subtracted
Tap two numbers, the result will take the place of the second.
Make the highest score you can.

- you can save the current game and start a new one, so that you can play up to 9 games at the same time.
- when you exceed 500 points, you'll be able to swap the numbers of two quartets of different color, dragging one over the other.
- customize the colors of the board with 351 different combinations
- you can also change the user interface color, light or dark