According to Jim (2001)

S04E17 The Mustache

When a stylish delivery girl offers Jim some trendy tips, he decides to sport a mustache, much to Cheryl’s dismay. In response, Cheryl dyes her hair brown, a change that Jim finds appealing. After an unexpected encounter with the delivery girl, Cheryl enlists her help to suggest fashion choices that would make Jim appear absurdly over-the-top.