I like the character switching mechanic with the gem toss, i also like how you used color only on interactive elemens of the game like characters and such and the rest is monochrome, it has that spectrum look to it with a modern touch like the smooth physics when you throw the gem and other objects.
Small issues still : the way you explained the controls i didn't think every character will have different abilities, so i got stuck for a while on the first level until i discovered that the green guy could double jump, once i figured this out i had a better time so the only small issue i'd say that remains is not having a quick restart button for when you fail to throw the gem on a character and after it stops you have to wait through the rest of the timer to try again.
Other than that it's quite fun and you've nailed the coop aspect especially in some later levels where you have to carefully understand which char can go where in order to clear the way for others etc..
Good job here :)