Inspect Red (#FF0000) in HEX, RGB, HSL, LCH and OKLCH, check its contrast, and copy the value you need.
Red
#FF0000
Black text reads best on this background, at 5.25:1.
Red is one of the 148 CSS named colors, and resolves to #FF0000 in every browser. In numbers that is rgb(255, 0, 0) and hsl(0, 100%, 50%). Perceptually it is a mid-toned, vivid color: OKLCH puts its lightness at 63% and its chroma at 0.258. It sits in the reds at 29 degrees of OKLCH hue, and reads as a warm color.
White text only reaches 4:1 here, so black text is the safer pairing at 5.25:1. At this chroma it is loud enough to be an accent or a call to action, but it will fight anything else vivid placed next to it.
The closest CSS named colors to Red, measured with CIEDE2000, are OrangeRed (#FF4500), Tomato (#FF6347), Crimson (#DC143C). If Red is not quite right, those are the nearest keywords to try before reaching for a custom value.
HEX
#FF0000
RGB
rgb(255, 0, 0)
HSL
hsl(0, 100%, 50%)
HWB
hwb(0 0% 0%)
CMYK
cmyk(0%, 100%, 100%, 0%)
LAB
lab(54.29 80.8 69.89)
LCH
lch(54.29 106.84 40.86)
OKLCH
oklch(62.8% 0.2577 29.23)
WCAG asks for 4.5:1 between body text and its background. On #FF0000 white text measures 4:1 and black text 5.25:1, so black clears it and white does not.
White text on Red
WCAG 2.2
4:1
APCA
Lc 69
Fails AA body text
Fails AAA body text
Passes AA large text
Black text on Red
WCAG 2.2
5.25:1
APCA
Lc 39
Passes AA body text
Fails AAA body text
Passes AA large text
Check Red against any other color in the contrast checker.
Red sits at 63% OKLCH lightness. Holding its hue and chroma and moving only that value carries it up to #FFF6F5 and down to #140000, which keeps the family recognizable instead of letting it drift toward gray the way a plain HSL ramp does.
#FF6452
20% lighter
#FF9080
40% lighter
#FFB5A9
60% lighter
#FFD6CF
80% lighter
#FFF6F5
100% lighter
#CA0000
20% darker
#970000
40% darker
#670000
60% darker
#3B0000
80% darker
#140000
100% darker
Build a full accessible scale from #FF0000 in the shade generator.
Hues rotated around #FF0000 in OKLCH, then pulled back into the sRGB gamut. Each swatch is labelled with the nearest CSS named color so you have a keyword to start from.
Red sits at 29 degrees. Rotating it a half turn lands on 209 degrees, the hue directly opposite. It is the strongest pairing you can make without changing lightness, and the one most likely to vibrate if you use both at full chroma.
The neighbors of Red at 359 and 59 degrees. They stay close enough to read as the same family, which is what you want for hover states, secondary surfaces and gradients.
29, 149 and 269 degrees divide the wheel into thirds. Balanced enough to carry a whole palette without one color dominating the other two.
Instead of the complement at 209 degrees, this pair flanks it at 179 and 239. You keep most of the contrast of a complementary pairing while losing the harshness.
Explore more combinations around Red on the color wheel.
The biggest shift is under protanopia, where #FF0000 reads as #271D00, 46.1 CIEDE2000 units away. If Red is the only thing marking a state or a series, roughly one viewer in twelve will miss it.
Protanopia
#271D00
Deuteranopia
#5E4700
Tritanopia
#FF0001
Achromatopsia
#363636
The nearest CSS keywords to #FF0000, ranked by perceptual distance rather than by how close their hex digits happen to look.