Very cool game! The minimalist art works very well, and giving color as a good ending is a nice touch. The game felt pretty hard to me, but it might be because I am really not a platformer player. I don't know if it is what was intended, but on my first run, I never got the speed boost because I did not go right at the beginning. It was mentionned before but the double seem to not trigger sometime for me; sometimes it seems it was because when the character is dropped if you jump right away it seem to count as the second jump but sometime it seem to be for another issue that I could not really pin on someone specific but it was pretty frustrating. Having the hitbox of the spike be more triangular so that you can jump over them even when starting close to them would have been less frustrating (but I've seen platformers implement it the same way as your game, so it might be a skill issue).
But despite the tiny parameters, the game has a very cool vibes and I spent a pretty long time playing (maybe a bit frustrated, but I still enjoyed it when I reached the goal)!