Andy, A light yellow baggy shrimp has been my best scud pattern down there. Make sure it is weighted as I have found that they really key into the proximity to the bottom. If the fly is too high in the water column they will snub it. If it is bouncing along the rocks and will come to rest on the bottom in current they well usually grab it. Yellow is about all I fish down there but others report that tan, green and orange work well too.
Mike
