“He mostly sees red where we see red.”
The normal use of the expression “he sees green where … ” is this: We take it as the criterion for meaning the same by ‘red’ as we do that as a rule he argues with us in giving the same names to the colours of objects as we do. If then in a particular instant he says something is red when we should say that it's green we say that he sees it differently from us.
Notice how in such a case we would behave. We should look for a cause of his differing judgement & if we had found one we should certainly be inclined to say he saw red when we saw green.
It is further clear that even before ever finding such a cause we might under circumstances be inclined to say this. But also that we can't give a strict rule for … .