I have a copy of Birds of the Puget Sound Region by Bob Morse which has some good colored photos. It could be a Cooper's or a Sharp-shinned which the book says are almost identical. The Sharp-shinned has "long, matchstick-thin yellow legs" & "long, square-tipped tail". The Cooper has "long, yellow, pencil-sized legs, longbroadly-banded tail".
So, I guess you need to catch it and check to see if the legs are matchstick-thin or pencil-thin. Good Luck.