Yellow (#FFFF00) is a very light, highly saturated yellow hue. Pure sRGB yellow is extremely light, so black text reads well on it but yellow text on white almost never passes contrast.
In RGB it is made of 255 red, 255 green and 0 blue. Its HSL hue angle is 60° with 100% saturation and 50% lightness, while its perceptual OKLCH lightness is 97% with a chroma of 0.211. For print, a starting CMYK mix is 0% cyan, 0% magenta, 100% yellow and 0% black.
As a text color on white, Yellow has a contrast ratio of 1.07:1, which fails WCAG AA even for large text. On black it reaches 19.56:1 and passes AA for normal text. If you use Yellow as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 101 for black text and Lc 0 for white text.
Its perceptual complement is #F4F3FF, close to off-white. Colors that look most similar are lemon, gold, mustard. It looks fairly similar to people with red-green color blindness (ΔE 2), so its meaning mostly survives.