This question was inspired by, and is kind of a corollary to, Could the star on favorited questions change in color?
"Important numbers" are usually displayed prominently on Stack Exchange sites. They include question scores (number of upvotes minus number of downvotes), answer scores, the number of users who have marked a question as a favorite, user reputation and comment scores. Most of those numbers are always displayed in the same color; comment scores are the exception.
Screenshot from Stack Overflow, 2011:
As illustrated by the screen clip above, the more votes a comment has received, the brighter its score is. (The 1 is gray; the 6 is dark brown; the 23 is light brown; and the higher numbers are orange.)
(Edit: it's now 2014, there are a lot more sites and the score/brightness correlation rule is no longer necessarily true. Screenshot from Meta Stack Exchange, this year:
Why is this system used only for comments? Should color-coding be expanded? Removed?