For Doreen,
Harlan's Hawks do occur regularly in western WA beginning in about October and continuing through March. We also have a lot of dark morph Red-tails here. The quickest way to differentiate between Harlan's/Red-tails and Rough-legs is to get a look at the tarsi (leg) of the bird if you can. Red-tails and Harlan's will be unfeathered, Rough-legs clearly feathered down to the toes.
I have never seen a dark morph Swainson's west of the Cascades and a Ferruginous, while possible, would be very unusual.
Incidentally, the claws of all NA hawks are black. The yellow you were seeing was most likely the foot, and maybe the tarsus, of the bird.
And to make matters more complex, there is now a movement to split Harlan's from Red-tails again.

Bud Anderson
Falcon Research Group
Box 248
Bow, WA 98232 USA
(360) 757-1911 (office)
(206) 962-7838 (cell)
bud at frg.org