The difference is very stark.

Check it out at the Dot Project (turn on the overlay in the lower left).

https://demographics.virginia.edu/DotMap/index.html

That line between green and blue between Warren and Detroit is 8 Mile Road, and yes the split between the south and north sides really is that stark.

Wayne County extends west to Livonia and Plymouth, which is a white, affluent, low-crime area. And south through a lot of other white suburbs.

It's completely believable to me that a random, non-discriminatory processing of rape kits would result in 86% of untested kits coming from people of color on that map.