You may be a person of color, but you're not black. What right do you have to tell me about racism? I mean, you're mixed, so you're half white!
I'm not sure that makes sense. Do you think people who are of mixed race can't understand racism?
Yes. It's just not possible that they can be treated as equal to every other person of color.
Biracial people can also experience racism. You shouldn't assume they don't because of their race. It's better to listen to people's experiences and believe them instead of denying harm they might have been though.