Seems like good dumb fun- something to kill some time with friends.
A few suggestions:
- If possible, add in a challenge mode- make the player tap a particular location, or temporarily make tapping lose you points, etc. I'd like something more than just "beat my last score"
- When the score comes up at the end, it's easy to accidentally close it. Maybe disable the buttons for a couple of seconds, or move the dialog to a place where the player wasn't tapping.
- The random colors are kind of distracting. It might be better with some sort of time based color- blue in the beginning say, but flashing red towards the end.
Best of luck!