Uh, hi! :) So, just use your arrow keys on your keyboard to move the rainbow ball, and try to not touch the black. The point is that you are a rainbow ball in a black and white world and you have to collect the rainbows so you don't turn gray.
ALSO!! Warning: The colors when the rainbow ball moves is pretty fast and bright. If you are not comfortable with that, don't play :) Also also, it does glitch sometimes... if it does then just reset by pressing the green flag! Have an amazing day!!