Well I wasn't really against the sky. I was mostly playing the devil's advocate. The problems with it I saw were:

the Halo was completely unknown at the time - not even the Monitor knew about it, so how would you even play on it? Avalanche even takes place after it's risen.

the sky is a huge part of a map - it would just be really awkward to be staring straight up at a planetoid that blocks the sky above.

also, due to the atmospheric conditions surrounding The Ark, the sky would have to be mostly cloudy red and dark orange. As seen at the end of The Covenant, when the ring rises, the clouds brush straight up against the structure. I think that a sky simiar to the one of "The Ark" would be best - blue, purple, "sand", etc.

F = Gm1m2 / d^2 is a big equation in this. If you are standing on the surface of Halo, you will have two Fg pulling down and one Fg pulling up. The two pulling down are closer together than the one pulling up, and since the force due to gravity decreases by the square of the distance, the Fg on the surface in this sky should be much greater (possibly 2x) than on Halo normally.