Any reason why the career badge is pink?
I noticed it on someones profile and it sparked my curiosity.
ChrisF and Anna Lear answered why it's different, so I'm not going to repeat them.
And Jin, Stack Exchange's designer-in-residence, would be able to answer definitively as to why it's specifically pink.
But I always understood the badges to be abstractions of the Post-It Note:
Badges awarded for upvotes received in a particular tag (such as career) have a different style to differentiate them from the other kind of badges. For example, I have a badge for the discussion tag here on meta and it's shown in pink as well.
As for why it's pink instead of any other colour... not a clue. That's probably a question only Jin ♦ can answer. :)