In the November issue of its Technical Journal, ICL includes a review of research into colour and its use in data coding on cathode ray tube displays which, although centred on the use of colours in graphical representations, raises the issue of the value of using colour for textual applications. After all, most advanced colour systems can produce 256 steps in voltage on each of three colour guns, enabling the generation of around 16.7m different colours – it would be nice to think that there was a real use for such capabilities besides graphical applications. The ability to use spot colour in text has been around for a century now, yet few publications make use of the facility mainly because it looks tacky and is hard on the eye. Is colour really any better than bold for highlighting? When IBM launched its first colour 3270 back in 1976, the colour red, associated with urgency or danger, was used to highlight important text the only problem being that red on screen didn’t show up at all, pushing the emphasised text into the background. The authors of the review, Darren Van Laar and Richard Flavell, of the Management School, Imperial College, London, admit that when colour displays were first developed, colour was largely used on a trial and error basis, whereas display designers now take the use of colour much more seriously, using it to liven up a bleak monochrome presentation, to reduce visual clutter by organising the display into perceptual units, or to code information. Studies conducted in the early 1980s tried to determine which combinations of colours on a display were the most legible and, although most of these studies used displays with comparatively low pixel resolution and a restricted colour range, they found that legibility was best determined by the luminance contrast between the colour combinations and between the background and the text. Interestingly, positive displays black text on a light background – are said to be better than negative displays because of their greater overall luminance which increases acuity and decreases the effect of illuminant glare.

Flicker

However, with bright, wide-angled displays with low refresh rates, flicker can be a problem. Other studies warn that colour semantics shouldn’t be ignored – implying that IBM was essentially on the right track to go for red as a highlight for important text – but legibility should not be neglected, relative lightness being the overriding factor. Nor should it be ignored that 8% of males and 1% of females have some type of colour defective vision – though this problem can be overcome by maintaining large luminance differences between colours that are likely to be confused. And it’s worth noting that the older you get, the worse your colour discrimination becomes, especially for the colour yellow. And colours from the extremes of the spectrum – red and blue – are reported to cause more discomfort, compared with those from the middle of the spectrum or white. But on the whole, users do seem to insist on buying colour displays over monochrome – one physiologist reckons that people may feel more secure using colour and rate their task as easier. Others conclude that colour improves acceptance of a new system within an organisation, and that computer operators prefer blue/green colour codes – but no correlation between colour and task performance has been found. – Susan Norris