What sRGB defines
HP and Microsoft proposed sRGB in 1996, and the IEC published it as IEC 61966-2-1 in 1999. It fixes three things:
- Primaries: red at (0.640, 0.330), green at (0.300, 0.600) and blue at (0.150, 0.060) on the CIE 1931 xy chart. They're the same as Rec. 709, the HD video standard.
- White point: D65, at (0.3127, 0.3290), a daylight white close to 6500 K.
- Tone curve: a short straight line near black, then a curve close to a 2.2 gamma. It spends more of the 256 steps per channel on dark tones, where the eye notices steps most.
Together they settle what any RGB value means as light, so #FF0000 is one exact red, not just the reddest red a screen has.
Why it's the default
CSS hex codes, rgb() and hsl() all name sRGB colors, and CSS treats an image with no color profile as sRGB. Most apps, SDR games and photos shared online use it too. A color outside sRGB needs a format that names a wider space, like color(display-p3 1 0 0) in CSS.
That's why sRGB is the range to get right first. Even on a wide gamut screen, most of what you look at all day is sRGB content.
What 100% sRGB on a monitor means
A monitor's sRGB number is usually coverage: the share of the sRGB triangle its own triangle holds. 100% means it can show every sRGB color, not that it shows them right. Accuracy, often given as an average Delta E in reviews, says how close each color lands.
A wide gamut monitor covers all of sRGB and then some. An exact DCI-P3 triangle covers 100% of sRGB, with an area 135.7% of sRGB's in CIE 1931 xy. Without color management or an sRGB mode, that monitor stretches sRGB content out to its own corners, and colors look too strong.