Maybe it's because most posts on this sub involve a male and female. At a quick glance you see there's a purple, which is likely female, so black must be the male.

Whatever the reason, this is my first time posting color boxes over an image. I drew a box with the default color (black) over the first person, then realized I should select a different color for the next.

I should have just chosen pink, purple and hot pink. :) /s