If an effect says that a creature loses hexproof or can be targeted as though it didn't have hexproof, this applies to hexproof from white as well.

Knight of Malice only gets +1/+0 if any player controls a white permanent, no matter how many white permanents players control.

"Hexproof from [quality]" is a variant of the hexproof ability. "Hexproof from white" means "This permanent can't be the target of white spells your opponents control or abilities of white sources your opponents control."