Here are some points from an Orp standards site, mentioning yellow legs as a fault:
Colour
The blue
Male plumage: Hackles,saddle, wing bow, back and tail dark slate blue. Remainder medium slate blue, each feather to show lacing of darker shade as on back.
Female plumage: Medium slate blue, laced with darker shade all through, except head and neck, dark slate blue.
In both sexes : Beak black. Eyes black or very dark brown, black preferred. Comb, face, wattles and ear-lobes bright red. Legs and feet black or blue. Toe-nails white.
Weight
Male: 4.55-6.35kg (10-14lb) when fully mature.
Female: 3.40-4.80kg (7.5-10.5lb)
The black
Male and female plumage: Black with a green sheen.
In both sexes: Beak, ect as in the blue. Soles of feet white.
Weight
Male: 4.55kg (10lb)
Female: 3.60kg (8lb)
The white
Male and female plumage: Pure snow white.
In both sexes: Beak, legs, feet and skin white. Eyes, face, ear-lobes and wattles red.
Weight
Male: 3.60-4.55kg (8-10lb)
Female: 2.70-3.60kg (6-8lb)
Serious defects
Side spikes on comb. White in ear-lobes. Deathersor fluff on the shanks or feet. Long legs. Any deformity. Yellow skin or yellow on the shanks or feet of any variety. Any yellow or sappiness in the white.
I'm not sure how much it would take to breed that out myself. Maybe someone could help here.