Well, the juveniles are speckled brown with no red breast for a start.
Sorry Steve my post was poorly worded, I know there is a difference between adult and juvenile.
Sandra for an interesting read try "The Life of the Robin" by David Lack whose work is still refered to and "Robin Redbreast" by the same author. They may still be in print, I think my copies are dated 1950,1953 which makes me feel old.
Hope this helps,
Chris.