Just found a ficlet I wrote on HPfGU back in 2000 (back when writing fanfic to make a point was not unusual on the list):
I would be surprised if there are no pictures in that photo album Hagrid
gave him of his dad in his quidditch robes, which would clearly indicate
which house James was in.
Can't you see it?
"My dad wasn't in Slytherin! I've got photos of him in his Quidditch robes,
and they're scarlet coloured, not green!" Harry pulled the photo album
Hagrid had made for him during his first year at Hogwarts out of his bag and
opened it to one of the early pages.
"But Harry," Draco drawled, "That photo was taken at the Halloween party.
He's obviosly dressed in a silly little costume. Your father was the
Slytherin Seeker. I know because I've got his old locker in the changing
rooms."
: tosses ficlet-concept aside in favour of canon. Oh well. Twas fun while it lasted.