Perhaps you should take your own advice. After searching multiple definitions of "racism" the closest that I could find to your definition was:

"a policy, system of government, etc., based upon or fostering such a doctrine; discrimination." which was the second definition referencing:

"a belief or doctrine that inherent differences among the various human racial groups determine cultural or individual achievement, usually involving the idea that one's own race is superior and has the right to dominate others or that a particular racial group is inferior to the others." This could apply to white people just as much as anyone else.

Regardless, your initial description of it being systematic oppression based on color in no way excludes poor treatment of white people based on the color of their skin. If a white family moved into a black neighborhood, for example, there could be plenty of social pressure on them if the black families around them were racist and even political oppression if the community was large enough.