Are you sure they are pencils?
Bill
When they were young, did they show the bronze pencil markings that moulted away? I suppose you could have very light pencil birds that would eventually produce an all white. White tends to increase in birds that show alot of white and all white birds can be bred from a number of combinations. This one would just be another possiblity. If you are certain that the parents are **** pencil, the white youngster should be as well. I'd test it with a more colorful pencil to see what happens.
Bill