Why yellow is uniquely difficult
The human visual system has peak sensitivity in the yellow-green range of the spectrum, which is why yellows appear perceptually brighter than blues or reds at equal saturation. This creates a paradox for UI designers: yellow is maximally attention-getting, but it also produces the most difficult contrast math. A mid-saturation yellow at 50% lightness, such as hsl(55, 50%, 50%) (#BFB540), reaches only about 2.1:1 against white, and pure #FFFF00 just 1.07:1 — both far below the 4.5:1 required for WCAG AA text compliance. Using yellow correctly requires understanding that its high perceptual brightness is a feature for attention states, not a substitute for contrast.
