The change comes as the Redmond, Wash., company is on the verge of shipping its Windows 8 OS, scheduled for late October. The logo change is intended to signify the "future, a newness and freshness," said Jeff Hansen, general manager of brand strategy.
Adding colors is intended to add "diversity," he added. It replaces a logo dating from 1997. Microsoft was founded in 1975 and had four previous logos.
Microsoft shares fell 29 cents to $30.25 in afternoon trading, valuing the company at $253.6 billion.