Well no actually, because it simply isn’t possible to be racist against white people, so the sentencing should be different to reflect that.
Racism requires a power relationship, that is for sure. But if someone is attacked because of their race (white) by someone not of that race (brown) then it is racially aggravated and should be treated as such.
If someone brown attacks someone white because they, oh i don't know, looked at them funny, then that's just twats. If someone white attacks someone brown because they looked at them funny - you'd have a tough time trying to prove it wasn't down to race, but it might not be. But i don't believe that "reverse racism" is A Thing. But i do believe that people of one race might target people of another race due to that difference. And that should always be considered an aggravating factor.