Fantastic job on your game! I love the whole aesthetic and the puzzles are very clever. There were a few times where I had to stop and think about how I needed to solve them. The music is very charming and the characters feel great to control, especially the fast green guy.
You added the keypress pause on new levels which is nice, but to increase responsiveness you may want to make it so that new key presses end this timer. If the player presses a key and nothing happens, then that can lead to confusion.
Your jumping is based on whether or not the player had jumping held down, which leads to a lot of awkwardness when you're trying to make that really long jump, so you hold jump the entire time and let off at the last second, but it's too late and your character jumps again. It's a big disconnect from what you wanted to happen and feels very awkward.
There's no feedback when you collect black's keys. This is especially imprtant on the level where you have to jump into the spikes to collect it. My camera snapped back to the orange character before I could register whether or not I collected it, and thus didn't know until I walked all the way over there with the orange character to see that, thank goodness I had and didn't need to restart the level.
Great job on this, it's impressive and a lot of fun to play.