Hey folks-
I occasionally lurk around here, and may never have posted before. However, there are a few things I thought I might be able to add for consideration. I've paid a good deal of attention to color perception partly because of some work I did in computer graphics and displays vs printed colors (like some others I saw) but also my interest in genetics, physics and colored gems- as will become clear.
First is that the human eye not only has the issues with focusing blue (and to a lesser degree, red) as described, but also has significantly different sensitivities to different wavelengths of light. The eye is much less sensitive to blue and red than mid-spectrum light (yellow). That is, if I have a nice, monochromatic 650 nm red light source putting out X watts of light energy, another at 450 nm, and a third at 530nm, the 530 nm yellow will look will look much brighter than the blue and red even if one can prove that the amount of light put out by each is the same.
BTW, the focus issue is that most materials will bend light different amounts depending solely on the wavelength- that's why prisms give rainbows. (in optics e.g. telescopes, camera lenses, and microscopes, this results in rainbows around things if uncorrected- when corrected the lenses are "achromatic") But different materials do it more than others- diamonds and certain other materials do it quite strongly, while crystalline pure quartz does is very very little (if you had 2 prisms, the quartz would give a very narrow rainbow, while the diamond a very broad one). In gems it's called "dispersion", and is the primary reason diamonds are so sparkly- you get lots of different colors out compared to e.g. quartz or sapphire. Good simulants like cubic zirconia or "moissanite" reproduce this quite accurately, some older ones (rutile, strontium titanate) are TOO sparkly.
The second is that the light interacts with various objects and their chromophores differently- a fine example of how funny absorption spectra of objects interacts with differing spectra of light sources and the uneven sensitivity of human vision to various wavelengths all come together to give color-changing gemstones: alexandrite (a rare chrysoberyl), and rare garnets, sapphires, and other minerals will drastically change their apparent color depending on the light source- usually shown as daylight vs. incandescent (or fluorescent vs incandescent). (in these cases the chromophore in question is chromium and/or vanadium stuck in the otherwise colorless crystal lattice... except garnets, which often have intrinsic color... and the compounds generally absorb mid-red and green but not long red or yellow) .
The same thing happens with lots of other subjects but is less apparent most times- but more than one author above noted that they saw lots of different colored leaves when the light changed from the yellowish incand to the blue-heavy LED. THis is really very, very common but hard to notice because people perceive only what they pay attention to- e.g., very little of the overall stimulus, and then its usually just a comparison between A and B, not any absolute measurement.
And different people have different light receptors and do in fact have different color perception- the most obvious is colorblindness- usually the lack of one of three color-sensitive compounds in the eye. Even though I con't perceive what you or someone else does, I can perceive and report that I can tell the difference between yellow, green, blue, and red in all the usual shades and intensities. Colorblind people simply cannot distinguish between certain shades of red and green or blue and yellow. BUT there are subtler differences, too- the eye has red, green and blue- absorbing compounds, and some people have different versions that absorb slightly differently- the light-absorbing compounds of the retina in some people absorb at different wavelengths even if overall they still allow for "normal" color vision by most tests. To such people, the colors of objects around the variant vision compound will appear distinctly different from "normal" people in that object X will look more or less different than object Y of similar hue and saturation. So a "normal" person would say that object 1 is closer than X to Y, whereas variant vision would cause the viewer to say that X is closer in color to Y than object 1.
Weirder still is people who have more than the usual three vision compounds- they can distinguish between more colors than we can because of subtle differences in the spectra coming from objects, usually in the green range (one lady could readily distinguish between paint and grass of the "same color" and even used different words when describing them, saying the grass was more like a nearby fence painted yet a third color of green that to the author did not seem very close to either the sample green paint or the grass). Birds generally have 4 such color receptors and in humans the condition is called tetrachromatism- google it for more discussion.
For gems, this all means that even non-color changing stones will have a different perceived color depending on the light source as well as on the viewer. Usually it doesn't really matter- but the next time you see a nice blue (real) sapphire, funny colored garnet (anything but pure "red" or "green"), try to view it under different light sources because it might look great (or crappy) under the halogens in the store, but look great in the fluorescent lights of the mall (and your work place), and in natural sunlight, still different depending on the time of day. I've got a few neat color changing garnets, and they vary from golden/plum to blue(ish)/red. Alexandrites (none of which I can afford) go from green to red, but other crysoberyls go from yellow to green. (all ordered sun or fluorescent vs incandescent) Neat, neat stuff.
So... It really is in the eye of the beholder. All you can do is get a light and see if it is useful under your preferred conditions.
Sorry for the long winded exposition, but I have an academic background (but by now, you're asleep I bet- I would be)
Ciao-
Nominally, Norman$.