Hey thanks for the feedback!
Have you tried switching to the 7th palette? it's really close to black-and-white!
I'll consider expanding it a bit to spice up the core loop, although I had in mind a very simple loop akin to Geometry Wars 2 - Pacifism mode when I was developing it. Maybe I'll add other modes or power-ups in the future.
High-score wise I've reached about x2000 multiplier (around 2 million points) in one game, I found it's easier to always keep the same colour and switch it only as a last resort :)