My google-fu failed me, and I couldn't find a simple colorizing pager that just dealt with basic spelling issues.
This is very much a stop-gap, because the real solution is to teach uemacs to do it, but I haven't touched that source tree in years and I wanted to test hunspell on something simpler first.
This is about as simple as it gets, without being so simple that it is useless. I can do
export LESS=-FRSX
export GIT_PAGER=huncolor
and the result is usable, and works reasonably well together with the existing git colorization.
And no, this does no context-aware coloring at all. Pathnames, URLs, this silly thing doesn't recognize any of that, just looks at things that might be words. In US ASCII only. What a crock.