no the white mustang knob exist proof
I don't believe those are stock Mustang knobs. The Mustang knobs are just like the Jazz Bass and Jag-Stang knobs. Like I said above, you can buy and add any knobs you want. Those are probably white dome knobs or Strat knobs. I am partial to Bell Knobs or Witch Hats, but domes would likely look closest to the stock ones, but white. You could always get white plastic spray paint and just paint them.
I would get these, but you can shop around.
All the different knobs.