"Most of the world's helium supply comes from underground fields in the United States."
Man, it must be hard to mine a gas, wtf. And why/how is it there?
"Many atoms emit or absorb visible light. In order to obtain a fine line spectrum, the atoms must be in a gas phase."
"All atoms absorb in the Ultraviolet (UV) region because these photons are energetic enough to excite outer electrons."
"inelastic scattering of light"
Why frequency gaps? Tetrachromats. Berlin and Kay
"In the 1969 study Basic Color Terms: Their Universality and Evolution, Brent Berlin and Paul Kay describe a pattern in naming "basic" colors (like "red" but not "red-orange" or "dark red" or "blood red", which are "shades" of red). All languages that have two "basic" color names distinguish dark/cool colors from bright/warm colors. The next colors to be distinguished are usually red and then blue or green. All languages with six "basic" colors include black, white, red, green, blue and yellow. The pattern holds up to a set of twelve: black, grey, white, pink, red, orange, yellow, green, blue, purple, brown, and azure (distinct from blue in Russian and Italian but not English)."
"The distinction between warm and cool colors has been important since at least the late 18th century but is generally not remarked in modern color science or colorimetry. The contrast, as traced by etymologies in the Oxford English Dictionary, seems related to the observed contrast in landscape light, between the "warm" colors associated with daylight or sunset and the "cool" colors associated with a gray or overcast day."
"Any color can be made to appear warm or cool by its context with other colors."
red-green color blindness
"Anomalous Trichromats are often able to readily spot camouflage clothing, netting, and paint that has been designed for individuals with color-normal vision."
""Mr. I. could hardly bear the changed appearances of people ("like animated gray statues") any more than he could bear his own changed appearance in the mirror: he shunned social intercourse and found sexual intercourse impossible. He saw people's flesh, his wife's flesh, his own flesh, as an abhorrent gray; "flesh-colored" now appeared "rat-colored" to him. This was so even when he closed his eyes, for his preternaturally vivid ("eidetic") visual imagery was preserved but now without color, and forced on him images, forced him to "see" but see internally with the wrongness of his achromatopsia. He found foods disgusting in their grayish, dead appearance and had to close his eyes to eat. But this did not help very much, for the mental image of a tomato was as black as its appearance."