The green, blue, and red squares in the Latest Reputation Received table on the Profile page denote the effect of the comment on your Reputation Score. If the rater approved the post, and at the time of commenting had a positive Reputation Power, the square will be green. If the rater had no Reputation Power the square will be blue. And if the rater disapproved the post the square will be red.
All of this is dependent on how the admin of the site, in this case Kurt or his staff, set the VBulletin reputation requirements up.
They can choose the colors too.