You’ve read all of your free items this month. To register, get added benefits and unlimited access to articles, Become a Member. Already a Member? Sign in. Advertising Age Article Abstract Watch Colbert Do a Top 10 List on Letterman That He Co-Wrote 17 Years Ago Plus, the Reason a Young Colbert Turned Down a Letterman Internship in 1986 By Simon Dumenco, Published on April 23, 2014 0 Want more Access, Content & Connections? Upgrade to Membership. We are glad you are enjoying Advertising Age. To get uninterrupted access and additional benefits, become a member today. Become a Member Already a member? Log in.