woa. that looks awesome ;) what am i looking at - whats the rule? and are you also coloring the spaces the ant has already been on, but that reverted to their original state?
It's not the most obvious UX but hit "/" to open the rules dialog, this rule set is "ant(2L 64F 2S)". Click through to the project page and check out the README for more info on the key binds: https://github.com/jcorbin/hexant.
The coloring trick is a recent addition I call "redraw tracing"; essentially there are two color palettes: one for "cold cells" and "hot cells" (ones that haven't/have been visited "recently").
What makes it "redraw" tracing is that "recent" is simply defined as "since last full redraw". Full redraws are triggered when the ant hits an edge of the screen.
I plan to expand the tracing to support "last-N" tracing where "recent" would mean something more comprehensible like "in the last 1024 iterations" f.e.