[IxDA Discuss] Amber and Yellow color perception

[Jeff Howard]

This is one of the few cases where George Miller's 1956 study "The
Magic Number Seven, Plus or Minus Two" actually applies. Based on
Miller's research I'd say that yes, most people are physiologically
capable of distinguishing between yellow and amber. But it's still
going to pose a problem.

http://psychclassics.yorku.ca/Miller/

Miller was studying the human ability to distinguish values along
unidimensional and multi-dimensional scales. Things related to color,
sound and taste for example. Basically, he found that most people have
the ability to reliably distinguish (by memory) about seven variations
on any particular scale. Some people are better or worse at this, so
the range is generally between five and nine variations. For example,
most people can distinguish around seven musical tones on a scale and
identify them when played without making mistakes.

With color it's not as clear-cut since colors often vary along
multiple dimensions (hue, value and satuation) but given a set of
colors that vary only by hue ranging from yellow to amber, people in
a psychology experiment could, on average, distinguish about seven
different variations in yellow/amber. Given that you only need to
make them distinguish two variations, that's well within most
people's perceptual threshold.

But outside of psychology labs people aren't in the habit of making
those kind of discriminations unless they know it's important. Most
of the time it's not, so people gloss over the details. Think of
traffic lights. Older traffic signals use a yellowish green for
"go" while newer lights use blue-green LEDs. If you asked them,
most people could tell the difference but they've probably never
thought about it. There weren't any publc service announcement to
teach people about the new blue-green lights because we're used to
those subtle variations being meaningless.

If you want a reference for how people _really_ behave (as opposed to
what they're capable of) then I'd suggest the writings of Herbert
Simon on the concept of "chunking". 

http://www.albany.edu/~dkw42/s6_chunked.html

In "How Big is a Chunk" (1974) Simon describes our tendency not to
attend to the overwhelming complexity of existence, but to mentally
"chunk" phenomenon into common patterns. I'd say that a relevant
example of "chunking" behavior is our ability to see the complexity
of the color spectrum as only seven (Miller) colors with the mnemonic
ROYGBIV. (And as far as I'm concerned you can throw out indigo--it
always seemed unnecessary.)

Getting back to your problem... If you absolutely had to use yellow
and amber, then make the distinction as pronounced as you can by
varying the saturation or value in addition to the hue (to the extent
that's possible with LEDs). Jim's suggestions about different
behaviors for the colors makes the distinction even more pronounced.
But it's safer to use some other color.