I understand the idea of voting for a great comment, but why does the comment's score change colors at five-ish up votes? Comment votes don't seem to give reputation, or anything else, for being great.
4It'd be nice if the "great comment" system was explained in the faq - I had to look at this question to find out what it meant.– SamStephensOct 13, 2010 at 1:03
See also How is the color for the upvote count on comments calculated?– PopsSep 26, 2012 at 15:46
All the votes do is help to visually identify good or insightful comments. You are correct, the color of the vote count does change at (IIRC) around 5 upvotes, and then again around 10. The specific color is tied to the site you're on; for example, the color becomes more orange on Stack Overflow.
Also, when the page initially loads, there will be at most 5 comments below each post. The rest of the comments can be expanded out, but the initial comments are the five highest-scoring.
Other than that, the score serves no purpose. However, I will say that even though I don't get reputation from a comment vote, I personally like to see that someone liked my comment and thought it was good or insightful.
For more information, see https://blog.stackoverflow.com/2009/04/comments-top-n-shown/
2The score changing colour upon lots of votes is a nice little touch, IMHO - a clear visual clue that the comment is "hot"– JonikJun 30, 2009 at 12:18
Why "around" 5 or 10 votes? Isn't it exactly 5 or 10? Jul 30, 2009 at 13:14
1@Daniel: I wasn't sure of the exact numbers. I'm pretty sure it's 5 and 10, but I don't know for sure. So I said "around". Jul 30, 2009 at 16:01
I still think there should be a badge, even a bronze one, for getting 10 upvotes on a comment.
5And now there is! Woo hoo! blog.stackoverflow.com/2009/07/reversal-and-pundit-badges Jul 13, 2009 at 22:45
Expanding on Kyle, the primary purpose of them was to get the best comments loaded on the page for all requests (instead of via AJAX) - so they can be indexed by search engines/visible to all users.