Yep, when doing retriever training, we use white, black/white bumpers for marking work, and use orange bumpers for doing blind retrieves. They don't see the orange, and pick up on the scent of the bumper when they are close to it.
Incidentally, most retrievers do one of the two retrieving types better. Either a dog is a good marker, or a good order taker, like what is required for a blind retrieve. Basically, when a dog is doing a blind retrieve, it has no idea where the downed duck is, so the handler sends the dog on a line to the bird, and constantly readjusts the course of the dogs by blowing the whistle, the dog then stops, faces the handler, sits, and awaits either a hand signal, or hand signal/verbal instructions from the handler. This is done both on land and water, at distances of 300 - 400 yards. It is quite a thing to watch some of these dogs. Amazing really.
I should explain marks as well. Generally, in an open division, 3 to 4 ducks are thrown in sequnce, some far 300 yds., some short maybe 100 yds. or less. Then the dog goes and picks them all up in sequence, or however the handler wants the dog to pick them up. Pretty incredible for a dog to remember where all 4 birds are, especially on water, when it could be 10 minutes or more from the time it was sent for the first bird to the time it picks up the last.
I highly recommend anybody interested in retrievers to get out to a field trial in your area, if you get a chance. You will be stunned by what these dogs can do.
) when it landed on top of a fence post beside a tree. 
