Exactly, but one seems to need to cross-compare with prosaic reports to establish that. (Both flags have Blue. Yellow should work as Ukraine's highlight, but probably best against Red (white would have its own type of layout ambiguity), for both that reason and at least another couple of reasons that might diverge from neutral 'nation-marking' ideals. Even if they're not the same pantone/RGB of Blue, pitting two blues against each other wouldn't be helpful enough, of course.
Going beyond the flood-fill is flag-inspired pattern-fill. Which probably can't be run 'straight' (even without
other potential complications, but left-slant blue/yellow striping vs right-slant red/blue/white (or similar cycling)
might work, with just a bit of care where isolated blues fall within the overlay of the opposing side.
A few overlaid labels/pointers to 'explain' particular bulges (could give date(-range) of a particular grab, for other useful data, or even point out a to-and-fro zone that actually expanded both ways/further-then-back, for which the final colouration gives no true justice (and could highlight your "as of today" clarification) could also resolve it, without much fuss.
Or an actual key, which would have made the initial view much less intruiging (as I quickly ran through a cartophilic/cartomanial internal monologue of what I would have done, of which the above is a much abridged summary) but left much of the ambiguity out.
This not being an issue with anyone here. Just surprised that the data-wranglers let such a potentially confusing thing go out without
some hint. (Probably orphaned from the general internal convention/key/explanation that they presumed all consumers would automatically have at hand/be familiar with by now.) I like my maps, and I can probably absorb more implicit truths from them than most, but you do often need
some explicit guide to visuals.