Neat little game! The concept is fairly simple and works really well!
The tutorial (which I read in its entirety before playing) was very confusing: too many colors, and too many mentions of the word "color" :P
But the great news was: I didn't need to know all of that! The gameplay is so fast and so clear that the only thing I need to know at the start is "try to go for the projectiles that are your color!" and the rest speaks for itself
(And if you were to change the shape of these projectiles from normal to a heart or a sort of power-up you don't even need to display a single line of text!)
Two things you could have done to make the gameplay a bit simpler (but that depends on your intentions of course):
1) slow down game time based on the top gauge, just like the music does. This gives you more time to think in a critical situation
2) I noticed when the enemies shoot a color they become that color. Why not the opposite? Make them change color after they have shot instead. This way you can anticipate who is going to fire your desired color (with a slower rate of fire as well)
The difficulty was good though. Not too easy not too hard. And the controls are smooth so if I lose it's my own fault. Good job with that :)
Music-wise the background music was a bit annoying. Some types of sounds lend themselves better to the "slow-mo" effect and this one was more annoying than helpful for me. Maybe a simple synth oscillator or a cool sci-fi beat (the dark tiled background reminds me of an oldschool space game). But this is understandable since you were alone on the project and the code and graphics are really good :)
Hope this helps! Keep on making them games!