I seriously doubt that racism plays much part in any effect you might think you see. I also question what you think is the evidence.
There might be some small effect based on language, not race. If a couple of academics at a US institution share a language other than English, they may be drawn together to ease communication. But such an effect should be short lived.
The fact is that the majority of US academics in STEM fields in the US are white males. The person in the next office is likely to be a white male. While there are issues with that, I don't see much racism in evidence within the academy. As with anything, there can be exceptions and a few noted scientists and mathematicians were notably racist. But they stand out.
The article cited by user Carl Christian on general self segregation can be easily explained. In the college first year student example, the self selection was going on before the students actually had a chance to meet anyone. So their self segregation was a result of factors outside the university not inside it. In the US, much of the force driving racism is fear of the other. We fear people who we haven't met and don't know. When a white and a black person pass one another on the street at night, both feel fear. But this fear is caused by the pervasive separation of the races in neighborhoods and schools. People have been actively discouraged from interacting in normal ways.
Fear of the other is probably much influenced by evolution. People in truly ancient times had to be wary when the met another person (from a different tribe) or an unfamiliar animal. Until you had some knowledge of how they would react, you had no basis for trust.
But within a university department, people do know one another and see one another each day and so have no reason to fear them. So, if you need to collaborate with someone you look first to the next office over, not thinking of them as different. They are just fellow academics. Likely they will be white men, of course. But if they have similar interests, regardless of race or sex, you will be glad to collaborate.
If racism and sexism exists in academia, and they do, it is much more likely to be evident at the point of entry, either for students or academic jobs. But after people come to know one another, assuming that is permitted and encouraged, the fear of the other goes away and we can just accept that people are people. The army doesn't give you the option of not participating. Initially you are forced to work with people not like you. But mutual trust is required for the job.
Since it wasn't referred to in the question, I didn't discuss the notion of racism toward students by faculty. Such racism might be conscious or unconscious, but it has a damaging effect when it occurs, regardless of cause.