"Make it more red." I've heard that request more than a few times in my design career, and everyone means something different. You could be looking at a colour comprised of 100% yellow and 100% magenta (the two colours that combine to produce red in process printing) and you'll still hear that request. "I can't," you plead, "it's as red as it can be!"

The problem lies in the fascinating (at least for designers) world of the colour spectrum, and different people's perception of colour. We each have an image in our head of what the ideal shade of red looks like, and that can lead to a lot of confusion when working on a design. Rob, our programmer, considers absolute red to be the RGB value FF0000, which is correct on an RGB backlit screen. I consider absolute red in printing terms - 100% yellow, 100% magenta. My old design director from a newspaper considered absolute red to be Pantone 186C. The average person would consider absolute red to be the same colour as an apple, a fire engine, etc.

Consider our language as well. A quick lookup of red in the thesaurus yields about 26 usable results, 11 of which could be considered primary shades: Falu Red, Scarlet, Carnelian, Venetian Red, Sangria, Maroon, Carmine, Vermillion, Burgundy, Persimmon and Magenta. A few years ago my wife bought a lovely red coat that was a wonderful scarlet. Now, a few years later, red coats are back in style, but in a slightly darker, understated Venetian red. Lucky for us, she cares more about literature than fashion or colour, so the (slightly) unfashionable red will continue to be worn for some time. Extra money will continue to be spent on books rather than the latest season's fashions.

Now add to this the fact that as many as 50% of women and 8% of men may have a genetic condition called Tetrachromacy, giving them four photopigments rather than three, and thus allowing them to see 99 million more colours than the average person.

Take a look at the two different reds above for a visual example. To many people they look exactly the same, however they're different by 4 dE (Delta-E) and specially trained or gifted eyes can perceive the difference.

Red is very seldom red.