Updating Comment Section Color

Hi - I've designed a website using the fixer theme, but I'm realizing when they create a new blog post it is using the color from the fixer theme's comment section. I'm having a hard time trying to figure out how to update this color so that eaCh time they write a blog post it uses their brand color and not the theme's original color. Any ideas?

You can see here: http://vivaciouscoaching.com/2015/06/06/test/

Thanks!
Liz