That a rainbow has seven colors — 'ROYGBIV' — was Isaac N... | funfact.wiki | funfact.wiki
That a rainbow has seven colors — 'ROYGBIV' — was Isaac Newton's choice. He first saw five in the prism's spectrum, but believing colors should number seven like a scale, he added orange and indigo. Indigo is the most disputed band today.
Purple does not exist in the light spectrum. When red and blue light simultaneously stimulate the eye, the brain creates this color to resolve the contradictory signals.
The "photic sneeze reflex," nicknamed ACHOO syndrome, causes people to sneeze when suddenly exposed to bright light. It's surprisingly common—affecting 18–35% of Americans and about 25% of the Japanese population.
In 1818, Siméon Denis Poisson argued that if light were a wave, a bright spot should appear at the center of a circular object's shadow — which he thought was absurd. But when Arago actually ran the experiment, the bright spot appeared, proving light's wave nature.
Hulk from Marvel Comics was originally gray. Stan Lee chose gray as a scary color unrelated to any ethnicity, but a CMYK printing error turned Hulk green in the first comic issue. Lee liked the result and made green Hulks official color.