Straightforward mechanics, well explained by the tutorial, (aside from a minor typo)
Nice graphics! Want to know more about the narrative, why am i this sprite that has to take gems to ghosts? Where are the ghosts going? Why are the gems endlessly leaving the chests?
My highest score so far was 18!
Maybe you could add a third colour (blue gem?) and then allow the player to save a gem (like saving a block in tetris) and switch between them. Sometimes i found myself holding a green gem and only red ghosts near me, but i guess that's the point xD