1.8 and beyond added void fog near bedrock level. This is not conducive to megabuilds that begin low. Fortunately there was a mod to remove it.
Unfortunately, 1.9 and beyond added a second effect when near bedrock: everything gets slightly darker. This mod removes both the fog and this second effect.
Vanilla Minecraft version 1.1 and up removes the fog if you are in creative mod (but not the dimming ugh). It also removes the fog AND the dimming if you are on a flat map. Use this mod to remove both of them no matter what: in survival, non flat maps, whatever
Creative Mode, no voidfog but still with dimming
See the images for an example of