Colour -- the treachery of colour -- part two

Checkerboard shadow illusion, squares A & B are
the same colour

©1995, Edward H. Adelson.

The image on the left is the best known web example of simultaneous contrast.which shows how our perception of a colour is altered by other colours in its vicinity. As the effect is due to relative differences in colours, it does not matter what operating system, computer, monitor or browser displays it. Even if your monitor settings are way off, the effect is still visible.

If you want to show definable, specific, colours on your computer screen, I'm sorry to have to tell you that your equipment is not good enough. Granted, you can compensate for the differences in the way a PC or a Mac shows colours by using the PNG graphic file type, but each piece of equipment is going to render colours slightly differently. You cannot even avoid the problem by having two identical monitors of the same model, built on the same day -- each one will show colours slightly differently.

If you are creating colours on your computer for use in the print medium, the problem becomes even greater because what is true for computer equipment is also true for printing equipment. In most cases, this is unimportant because the majority of commercial colour printing uses process colours in four-colour separation. These colours are restricted to specific ink formulae but not all colours are possible with this method: as the "M" in CMYK is magenta, a pure red is impossible with this method. Usually, none of this is terribly important because your eye and brain will change your perception toward what is expected.

Now, if we assume that colour psychology is a real phenomenon and hypothesize that the effects are measured by wavelengths of light, alone or in combination, then creating new non-process colours becomes a huge problem. The ideal printing environment is CMYK, but computers all render colours using red, green and blue (RGB). If you mix red, green and blue paints or dyes you will get a muddy gray colour, but if you mixed the same colours in light you would end up with pure white, and if you mixed red and green light you would get yellow. In some graphics software, you can detect which of your colours are not in gamut. You will know right away that those colours will not be displayed properly in process colours.

When I was creating emergency evacuation flood maps, I learned that colour psychology was an important factor -- my maps had to be used by people facing a disaster and it was important that the maps be not only very clear and easy to understand, but also should give a calming effect. As I was working on a computer, and creating new colours in RGB, I actually had to work blind. Not only that, but there is no mathematical formula that I could use to get the colours just right. I picked a range of RGB colours for the palette that delivered the sort of effects I wanted, then varied each one slightly by alternating between RGB and HLS to create a set of similar colours. Next, we sent this colour test file to a commercial printer after arranging for a single machine to be dedicated for the entire project. Once, a  company decided to sell of one of their machines as they had two of the same model and the workload did not justify having two of them. Sadly, they picked the printer we were using to dispose of (without telling us). I discovered the problem on the very next print job -- the colours were wrong. We decided to go with a new company after that. It was not just the colours that were important but the maps had to contain more levels of easily perceived data than are considered possible and I used simultaneous contrast and ordinary contrast to achieve that. The maps also had to stand up to being photocopied in grayscale without losing the contrast effect. My maps differed from all other maps, most noticeably, in how all of the grid lines showed the same contrast regardless of what colour or tone was beneath them.

The company for whom we were creating the maps violated our contract, thinking that they could do it themselves. After a year of trying, they had failed to create a single map. The process was so complex that it was impossible to reverse engineer. At first, the engineering company they used to compile the flood data thought that my maps must be inaccurate because they were so pretty. The engineers seemed sure of that fact -- to the point of being smug about it. We let them proof read a sample to make sure that the map was accurate. Although my spatial perception is excellent, we had a young Vietnamese man whose spatial perception beat my own, hands down. He could spot a dot that was a single pixel out of alignment! The psychological effects worked very well -- my wife noticed that people's voices became softer and calmer than usual when they were looking at a map.

This will be an ongoing and irregular series on colour. One of the upcoming episodes will be about how the colour wheel is all wrong. Have a great weekend -- I'm waiting for a couple of interesting examples of early Celtic art to be delivered -- at least one of them should arrive next week and I will publish them both here.