As I understand it, he has said in the past that the white cassock is what they wear in India, and since Fr. Pfeiffer is still officially assigned as an SSPX priest in India, that's what he wears
Yes, white cassock is normal for missionary priests in hot climates. But in the US, I don't think a missionary priest would keep wearing the white cassock unless it was for a short trip (fundraising), or he recently moved to the US permanently and has no other cassocks yet.
The sash, however, makes him look like a missionary bishop.
Or perhaps the color is a perception illusion like the blue/gold dress?