Only being able to change colors on the beats was kind of neat (maybe set it up so you don't have to be perfectly on beat, but maybe being closer to perfect increases the combo more), but it didn't really feel right for the dashes (maybe instead of only being able to dash on the beats, a dash could deduct from the combo or something instead). 1 hit to a game over felt a little too punishing. I think like 3 hits (even if a hit started the wave over or something) would've been more reasonable.
Anyway, there's some interesting ideas here and it'd be cool to see what you come up with if you decide to develop this out a little further.