Individuals overcome racism by doing whatever it is they do to do so. Overcoming the obstacles that life presents is exceedingly difficult for everyone; in the history of the planet. That is life. If you identify yourself as a group, rather than an individual, then you buy into the group. The group may be wise or not, but individuals have wisdom available to them if they simply understand themselves. Groups can't access wisdom ; only individuals can.
The common ground that my OP talks about is our human nature. It is a subject that gets so little attention but so desperately requires attention. Individuals access an understanding of themselves, and therefore everyone else, by painstakingly honest introspection.
Just as a side note: racism exists because people are people. There is always an us and them attitude throughout life. My religion, your religion....my color, your color... my country, your country....my town, your town....my sports team, your sports teem..... etc., etc, etc
It is up to the individual to figure this out and carve a way through life.
Most humans are lazy when it comes to trying to understand themselves.