Should the color_belly tags even exist? People keep tag it which adds the implication belly on posts with flat abdomens.

From the tag description, those tags are used to describe a character's color patterns. It makes sense to me for these tags to exist. (Ex: blue_belly has "Used for posts depicting a character with a blue-colored belly." and is aliased from blue_stomach).
I think the tags should stay, but the implications to belly (character has a protruding belly) should be removed. "Character has X color on their abdomen" does not imply "Character has protruding abdomen".
Make a BUR?

*_belly tags are in a sort of limbo. They include midriffs but belly doesn't, so they can't imply it (see hand on belly, cum on belly, holding belly)

The precedent is just to remove the belly implications from them, but there are other options.

We could have a separate *_belly and *_midriff tags, and/or create an umbrella tag for both (with a better name)

If we're talking about countershading, [color]_countershading + countershade_torso is what I'd consider the right approach. We already lost countershade_chest as a unique tag, so I suspect the Powers That Be aren't going to be on board with having a unique tag for midriff color.

errorist said:
If we're talking about countershading, [color]_countershading + countershade_torso is what I'd consider the right approach. We already lost countershade_chest as a unique tag, so I suspect the Powers That Be aren't going to be on board with having a unique tag for midriff color.

Yeah, it's rarely just the belly that's its own color, it usually consists of at least the chest too, if not also the inner thighs, under-tail, and neck. Continually tagging <color>_belly, <color>_chest, <color>_neck, etc, all with the same color on most posts would be tedious and bloat the tag list. Better to use something like <color>_countershading + countershade_torso, which can cover the belly and chest area, as well as optionally the neck and muzzle, inner thighs, and under-tail.

I could see keeping <color>_belly for only when the belly is a distinct color from the chest, back, and crotch area, but if history has shown us anything, there will be people that'll wantonly apply tags like without checking or caring about the nuance the tag is supposed to have.