The colour will be written in the center of the screen. If the colour matches the background, TAP. There is easy medium and hard modes.
Easy- 30 levels, 3 seconds per level
Medium- 50 levels, 2 seconds per level
Hard- 75 levels, 1 second per level
There is also survival mode in which, rather than a set number of levels, you keep going until you get 5 wrong!