If Cerus Beta doesnt have an atmosphere, it shouldnt have a blue sky. I think that a perpetually black sky would fit the “end” theme better as well. It would look cooler and more alien, and considering that literally every planet has the same sky (other than cerus alpha) I think that even a little bit more variety would be nice.
I think this may be hard to do without setting the time to be set as night or early morning/late afternoon permanently, however it is a good idea.
I was thinking more along the lines of an end biome (or “space”, i guess) sky, rather than keeping the overworld sky and permanently setting the time to night. Idk how easy or possible that would be, though.