They show the color order that Peeps have been released in. Blue was the 1998 75th anniversary color.
Peeps are really quite fascinating.
In the beginning, Peeps were handmade and took 27 hours to make just one. Peep eyes are virtually indestructible. Vegetarians shun Peeps because of the gelatin used in making them. So, here now are a few of what I consider to be the finest of Peep links. The Official Peeps Website - this site includes the history of Peeps.