Features for the sake of features presented by Mark Zuckerberg's social media is from time to time. The goal, of course, to make users more comfortable and reluctant to turn to other social media.
For this colorful comment feature, like the nickname allows you to color the comments you post. But this kind of feature is not a new thing on Facebook.
Only before that can be colored only the status to be posted, not writing comments. To display colored comments, you simply follow the same way as when coloring the status.