most have already said it, but as the game gets bigger, there will need to be some indication of important elements in the room other than just color. Keys are the only one that this build needs, but later mechanics might also need the indication. As for increasing complexity, routes that require going though different colored locks (and multiple rooms with the same colored key) can really make planning the route harder. An example would be to put an upwards exit in the green room, but then comes the complication of making sure players dont softlock themselves by falling from the top without the tools to get back up. maybe a reset button, or adopting the powerup systems of other metroidvanias?