Apple has admitted that some of the screens on its new iPod Touch have trouble displaying dark images.

IPod Touch customers began complaining on Apple's forums soon after the launch that video was so dark that it had the appearance of being reversed out in some areas.

Wall Street Journal columnist Walter Mossberg questioned Apple about the complaints and was told that only a "small number of units" were affected and that the issue is "being remedied".

Some customers have also complained about being charged a re-stocking fee of $30 or $40 on attempting to return a faulty Touch, only to be told that the device was working properly.

It is still unclear what causes the problem or how many units constitute a " small number". Apple has not said whether it will be replacing the affected units for free.