To break down white supremacy in the UU hiring context, it is an unspoken (but indefensible) assumption that because UUism is "predominantly white", UU religious leaders who are white will be more effective leaders, a better fit, more likely to be team players with the rest of the leadership and less likely to run into problems with our mostly white congregants and congregational leaders.
It is also an assumption that investment in creating congregations of color is very risky and most likely to fail.
It is also a white supremacist assumption that most people of color are not interested in a religion like ours, therefore UU religious professionals of color are doomed to failure -- unable to minister to people of color outside our congregations and less likely than their white colleagues to minister effectively to the white people in our congregations/communities.
These assumptions lead inevitably to the unspoken conclusion that when it comes to hiring religious leaders for the UU movement, white is better!
This whole train of assumptions and conclusions are based on the idea that liberal religion and Unitarian Universalism are culturally appropriate to white people, but not so to people of color. It's white supremacy, friends.