So... Why not just strike a balance between #6123 and #8468 instead, and have non-colourblind vulp/taj have see_in_dark of 3-5, and keep colourblind vulp/taj at 8? (Or if you would rather go the nuclear route, just do 3-5 for vulps and tajs in general)
Another interesting idea is #8688, but it died because the coder couldn't port it. Perhaps someone could have another crack at it? (I know, WYCI, but I do believe that this might be a way to solve the darksight issue.)
This is also a problem - If darksight is entirely removed from vulps, then they literally have nothing going on for them in terms of boons/maluses other than +11% hunger and claws. Flash vulnerability is usually pegged as a malus to darksight, so there would need to be more boons/maluses for vulps and tajs.