Color abnormalities don’t seem to be very unusual in juncos. There is a junco who sings outside my work building who has white splotches all over him! None of the juncos we’ve caught have been that extreme, but we have found a few with unusual spots of color on them.
SOMA has a white spot above his right eye:
MANI has partial white eye-rings:
And NOLA has tufts of brown feathers (instead of black) right by his nostrils:
I love these little differences between our birds.