I'm sure someone will come along and correct this, but the whites are pretty rare.
I hatched out a Splash Sumatra from blue x blue pairing-I believe the white can be a result of a Splash x Splash pairing.
The whites and splashes are not accepted varieties of the Sumatra at this time(not sure if they will ever be) which is why you don't see them at shows.
White Sumatras are beautiful, but they are not particularly desirable by serious breeders.
If I had one, I'd keep it around just for my own enjoyment.
Like I said, if this information is incorrect, someone will come along and correct it.