They are linked by they used to do it by there color of there skin as well
"His or her" would technically be the best fit, since it is acknowledging both genders, but it is very common to use "their" any most people wouldn't consider it wrong. <span />
When attempting to clear to a reader and appealing to their understanding, using examples and academic, clear diction are very helpful. Examples back up your points and leave open space for explanation and commentary that would further the readers understanding, and your word choice is what sets the stage for what you are writing about.
I hope this helps! :)
