Mr. Colson is one of two executives considered by many to be heir apparent to the Callan throne. The other, Greg Allen, is executive vice president and manager of specialty consulting.
Mr. Colson has worked at Callan for 12 years. His group advises more than 150 money manager clients, including Artisan.
Artisan, Milwaukee, is a domestic and international equity manager with $40 billion under management. Mr. Colson will work in the firm's San Francisco office.
Calls to Mr. Colson and Callan Chief Executive Officer Ronald Peyton were forwarded to the firm's public relations office; PR staff did not make either man available.
In a letter to the firm's money management clients, Mr. Peyton said Sue Crotty would replace Mr. Colson. Ms. Crotty, a senior vice president, has been working with Callan's East Coast money management clients for almost three years.
"Sue brings a wealth of energy, creativity, intelligence, salesmanship and experience to her new position," Mr. Peyton wrote.
Some insiders said Callan's plan sponsor clients might question its strong recommendation of Artisan over the past several years. Reaction to Mr. Colson's departure, however, was mixed.