An iMac owner is suing Apple Inc., claiming the company's 20-inch iMac desktop computers can't display the "millions of colours" Apple promises in promotional materials.

The lawsuit alleges the Cupertino-based company touts that ability on its website and in other marketing material even though it knows iMac monitors can display only 262,144 true colours.

The suit was filed Monday in the U.S. District Court for the Northern District of California.

Users are fooled into seeing many more colours because the monitors use technological tricks that involve showing many similar shades at high speeds to create the illusion of the desired shade, according to the lawsuit.

Those techniques can cause "crippling" problems for people editing pictures and videos because the colours don't always appear entirely smooth, the lawsuit said.

"Apple is duping its customers into thinking they're buying 'new and improved' when in fact they're getting stuck with 'new and inferior'," said Brian Kabateck, managing partner for the law firm that filed the suit, Kabateck Brown Kellner, in a statement.

"Beneath Apple's 'good guy' image is a corporation that takes advantage of its customers."

The plaintiff, Texas resident and iMac owner Chandra Sanders, is seeking class-action status for the lawsuit.

The lawsuit targets the 20-inch aluminum iMacs introduced in August 2007, saying the 24-inch versions are capable of representing millions of colors.

Apple said it doesn't comment on pending litigation.

The company in 2005 settled two different class actions on its iPod music players. One dealt with the iPod's battery and another claimed the screen of the Nano iPod was too easily damaged.