About Yellow
Yellow is the most luminous hue at full saturation — #ffff00 reflects more light to the eye than any other pure color, which makes it both the best highlighter on Earth and the hardest color to read. Its entire design life is a negotiation with that brightness.
It is the color of sunshine and caution simultaneously: the same wavelength that says optimism on a smiley face says “wet floor” on a sign.
History
Yellow ochre is in the oldest cave paintings; Indian Yellow was (legend says) made from the urine of mango-fed cows; chrome yellow gave van Gogh his sunflowers and school buses their federally mandated color — National School Bus Glossy Yellow, chosen in 1939 because black lettering on yellow is legible earlier in peripheral vision than any other combination.
Psychology
Yellow triggers the fastest visual response of any color, which is why taxis, road signs and warning tape claim it. It rates highest for optimism and lowest for luxury; overuse measurably increases visual fatigue and even infant crying in yellow rooms — dose it like seasoning.
In design
Yellow text fails on white catastrophically (1.07:1 — the worst pairing in the palette) and yellow backgrounds demand near-black ink. On dark UIs, amber-yellows (#facc15, #fbbf24) are superb attention accents. Pair with black for maximum-urgency signage, with navy for nautical class, with gray to calm it down.
In culture
Yellow is imperial China’s exclusive color, Buddhism’s golden robes, journalism’s slur (yellow press), cowardice (yellow-bellied) and friendship’s rose. In sport it is a warning card; in cycling, the greatest jersey there is.