Q I bought a new iMac, and have since noticed that the display flickers slightly, particularly when the brightness is turned down. The whites then also look slightly dirty, with a tendency to yellow towards the bottom of the screen. Should I be worried about these? Is there a solution?

A You should try to perform a proper display calibration, preferably using an external calibration device such as a ColorMunki or Pantone Huey, and see whether you still notice these effects at the normal brightness level with your display running on the custom profile.

If you have any remaining reservations about the quality of your display then, do not hesitate to contact AppleCare: Apple has recognised that some displays have problems with colour casts (particularly yellow) and you may be entitled to a warranty repair.

Flicker is more complex but used to be easier with CRT displays, depending on refresh rate, screen phosphor persistence, and the viewer. Flat screens are different, as being digital they are not prone to the same types of electrical interference, although some individuals do still find that certain displays appear to flicker. This can be ameliorated by adjusting ambient lighting, and sometimes is exacerbated by fluorescent (tube or long-life ‘bulb’) lighting nearby. Experiment with ambient lighting to see if you can reduce the effect. This could also relate to a problem that needs to be corrected in a warranty repair, so you may wish to raise it with AppleCare.

Updated from the original, which was first published in MacUser volume 26 issue 10, 2010.