I don't know if you want to hide the first aid block when it is dark, but using the robot's wholly black palette like Espozo said does not only help hiding it, but would probably also help make the exit sign more believable once the unreal light of the box is gone.
Also loving the backpack keeping in the sauna. And, well done on the glass wall. It stood out to me as really good looking.
Sharing a technique: It is a common practice in film animation to let components of a unit lag one up to several frames behind each other, anywhere one component is the force that pushes the other into action.
1)When the main character is riding the bike, the vibration of the vehicle would (in the real world or in a cartoon) make the character bump - not in unison, but in cascade. This would've been easy to implement on a system with less sprite restrictions, of course. Attempting this on large nes sprite groups might need to involve tile-level animation.
2)When the finger is pushing the button, there is a span of travel for the finger to do before the actual pushing takes place. This may be simulated with a similar cascaded lag.
The sense of pre-signaling movement prepares the audience to both focus on and accept the action about to come. In the examples above, the actions are pretty self-explanatory, though, so it's mostly for appearance; to heighten the naturality or hide the animator's hand.