Owners of the latest Apple iMac desktop computers are reporting yellowing screens to add to a number of issues highlighted by unhappy customers, amongst them flickering and broken screens.

"The colour of the image on screen is tinted yellow. The severity varies, but in some cases is reportedly bad enough to render the computer essentially useless," Daily Tech reports

Tech site Gizmodo has also noted a new wave of iMac complaints. "Yellow screens and flickering screens are both persistent problems, still being reported by our readers, that no firmware update has fixed," writes Gizmodo's Mark Wilson.

"One extremely tech knowledgeable reader wrote me after dissecting his own yellowed iMac. He dug around inside the monitor and colour temperature tested all of the machine's LED backlighting. He said that the LEDs all read about 9300K, which is, in fact, very, very cool (think blue, not yellow), and brightness readings were normal as well," Wilson notes.

"Then he confirmed his findings on another yellow iMac, recording all LEDs as within expected thresholds of +-10mcd brightness, +- 20nm in colour. So from what we can tell, iMac displays don't have an LED problem - which certainly comes as a surprise."

A thread on Apple's support forum dedicated to the flickering screen problem has been active since late October 2009. Customers concerns prompted an independent website, Apple iMac (Fall 2009) Issues, to be set up to keep track of issues.

"I received a new iMac today (my third so far) and it has a very yellow screen. Some photos and notes can be viewed on the yellow tinge page," the Apple iMac (Late 2009) Issues website reported last week.

Apple started delaying shipping of the new 27-inch iMacs models before Christmas according to reports from authorised resellers. The UK Apple Store is currently still showing '2 weeks' for delivery for the 27-inch: 3.06GHz and 27-inch: 2.66GHz Quad Core models.