HueComb

Red

#ff0000

A red that is about as vivid as sRGB can show at this lightness. It is light — black text sits on it comfortably, white text does not.

Hex

#ff0000

RGB

255, 0, 0

OKLCh

62.8% 0.258 29.2°

CIELAB (D50)

54.3, 80.8, 69.9

What is true of this colour, and of no other

  • 31 other named colours sit within ΔE00 2 of it — this part of the space is crowded, and the names here are finer distinctions than most people make.
  • It sits exactly on the sRGB boundary: at this lightness and hue the gamut has nothing left, and a wider display would show a more colourful version of it.
  • As text on white it measures APCA Lc 64.1; on black, Lc -37.5. The sign is the polarity, which the WCAG ratio discards.
  • Built into an eleven-step scale, 10 of the 10 adjacent pairs stay ΔE00 2 apart — see the ramp.
  • protanopia and deuteranopia and tritanopia shift it by ΔE00 45.2 and 47.2 and 51.7 — no red cone.

Text on this colour

White text

4.00:1 — large text only

Black text

5.25:1 — passes AA

Black text is the better of the two at5.25:1. That is enough for body text.

As text on white, it needs to change

#ef0000 is the nearest colour of the same hue that passes AA on white, at 4.50:1. Only the lightness moved, and some saturation was given up to stay inside sRGB.

Try it against your own background

The same colour, with one cone missing

As you see it

#ff0000

protanopia

#5e5e0d · ΔE00 45.2

deuteranopia

#939300 · ΔE00 47.2

tritanopia

#baba00 · ΔE00 51.7

Run a whole palette through all three

The twelve nearest named colours

Ranked by CIEDE2000 — perceptual distance, not hex arithmetic. The closest isRainbow’s Outer Rim at ΔE00 0.099: below 1.0 — an ordinary observer cannot tell these apart, even side by side. What the numbers mean.

3 of these have no page of their own: pages exist for the 4,961 colours the dataset marks as good names.