every fox kit that i've seen in the past 2 weeks (about 8 or so) have all been red with black feet and white tipped tail....just like mom & dad.
but.....there is a melasic or cross fox running around about 3miles from my house, i wouldn't doubt that if it had kits they too may have that dark coloration.
another possibility is that a female red fox in your area came into heat late...or was bred late in the winter. and she just now had her kits. when red fox are first born they have a brownish coat with white tipped tail. but, the only problem with that is...i think that the kits would have grown into their red coats before mamma would allow them to adventure out of the den.
did you see a kit close to a den...or out milling around?