It might be cool to make health as part of your energy too , so that you only have one resource to juggle around(and healing pick ups are much more needed which push player to venture out to darkness) perhaps even add in doom style where enemy will drop pickups at higher rate when your energy gets low!
Any way , cool take on the only one color concept. I made a one color game too : https://itch.io/jam/gmtk-2019/rate/460289