The colors on each participants tag represent the event they are competing in. Marathon, half marathon, 5k's, etc. For your first marathon, your color is blue. And it even says, "my first marathon on it". I love this!
I found this article on the Route66 website and it really meant a lot.
My First Marathon Numbers
"Participants who pre-registered that are participating in their first marathon at the 2009 Williams Route 66 Marathon will receive blue race numbers. We highly encourage you to give them special recognition when you see them. They have all worked very hard to get to the start line. Training for and completing your first marathon is truly a life changing experience and disserves special recognition."
-Not, sure about the special recognition part (every participant is conquering a goal) but the rest of the article was really touching!