Griffin,
We did update the JFBCSocial plugin to be able to include a separate CSS file, but for now, it's only when the content plugin is set to hide the Like button. We use the CSS to hide the like button, but don't change any of the color scheme using the CSS file. It's a little confusing, I know. If you're using the content plugin to insert the comment box, and have the like button disabled, you should be able to edit the /plugins/system/jfbcsocial/fb_comments.css file and change the text color easily. If so, let us know, and we can help you with what you need to update.
Right now, there's unfortunately not a parameter to force the loading of a separate CSS file or change the color easily. So let me know how you have things configured, and we'll figure out a solution for you.
Thanks!