Your "White" mulberry was red in color?
Idk... From crfg website: The white mulberry is so-named for the color of its buds, rather than the color of its fruit. I am really hesitant to keep this variety. Definitely cannot compare to regular pakistani (my rootstock).
There is a "white pakistani" fruit from another graft that has been overshadowed, hoping to taste that one soon. If that one is sweet, then I can more or less conclude it's the variety, not timing.
My rootstock is regular pakistani, and this spring I grafted noir de spain, this unknown "white", and "white pakistani" onto it. My priority is taste (namely sweetness lol), then staining potential.