I think the main reason you don't see People of Color (POC) in the floss community is the same reason you don't see lots of black folks in lots of other industries.  POC have been purposefully kept out of tech jobs in America!  It's the same reason you don't see women in many of these places as well.  
I would postulate that 'many' of the people who contribute to Floss also work in tech in some way or another.  (Notice the word 'many'...not 'all' or 'most')

Just so you know...  I'm black man, US citizen who lives in New York
City. I work as a software engineer and I'm also interested in Floss.

blizzack.com