Purple, Reddish Green and Other Forbidden Colors

Tyrian Purple was the original ‘forbidden color’.

It was so difficult to produce this dye – 12,000 sea snails were required to color one garment – that royalty would execute anyone else daring to wear it.

It wasn’t until the late 1800’s that chemistry made a cost-effective purple dye a reality. Purple still retains some of its mystique – Prince sure likes it still – but you couldn’t call it forbidden today.

###Forbidden colors today

Today we all know there are sounds that dogs and elephants can hear, that we humans can’t.

Likewise, there are colors that our standard ‘eye hardware’ can’t normally perceive – at least not without help. We call them forbidden or impossible colors and they include reddish green and yellowish blue.

Back in 1983 visual scientist Hewitt Crane conducted an experiment showing subjects parallel, adjacent blue and yellow color strips. Eyetracking technology kept these strips in precisely the same position on the test subjects’ retinas.

As the color receptors on each part of the retina tired, users reported that the border between the colors had melted away, giving them the sense of a new, never before seen color – not a green but a ‘yellowish blue’.

“It was like seeing purple for the first time and calling it bluish red”.

In a similar way, in you should be able to momentarily see an impossibly dark blue circle as the yellow graphic disappears. Stare at the black cross and relax.

I know what color I’m asking for in my Apple Watch.

###Manipulating Color in The Real World

So does this have any use in the real world?

Which company would you expect to bend this science to their own ends? Coke? Google? No, in fact it’s those mad scientists at Disney, of course.

Arriving at their Epcot Center you might momentarily notice the wide, pinky-terracotta terraces that lead you into the park. As you follow that path the red receptors in your eyes fire repeatedly “RED! RED! RED! RED! RED!..” That color choice is no accident.

As you continue following the path those red receptors begin to get tired. “RED… red… red… re…”.

When you finally look up at Epcot’s lush vegetation your red receptors are exhausted, and your brain is instantly flooded by signals of impossibly lush, greens. A rich, verdant paradise.

Pretty crafty, huh?

But it’s a potentially powerful idea and something that could be used to good effect in your design.

Originally published in the SitePoint Design Newsletter.


Purple/blue hues are still difficult for modern day camera sensors. Its the one area digital photography still has a problem with for accurate colour reproduction.


Whoa. I can’t figure out what the craziest part of this article was: that some guy bothered to collect 12K (!) sea snails, that people were executed for it, that I saw a new color, or that someone figured out a real use-case for it…


Oranges were always a problem when I work in 4-color printing. Bright oranges would turn flat mustard when you printed them. I think it was a problem with the purity of the inks used. You could make better inks but they were much more expensive to produce.

Maybe it’s similar with camera sensors and purple?

1 Like

I find photographing purple works best against a gray background, and adjusting white balance settings. There aren’t any specific settings I can give you, as it depends on the camera’s quality, the depth of the purple shade and the overall lighting situation. In my experience true reds and purples are difficult to photograph with most smartphones and low-quality digital cameras, but has gotten better over the years.


This topic was automatically closed 91 days after the last reply. New replies are no longer allowed.