Inspect White (#FFFFFF) in HEX, RGB, HSL, LCH and OKLCH, check its contrast, and copy the value you need.
White
#FFFFFF
Black text reads best on this background, at 21:1.
White is one of the 148 CSS named colors, and resolves to #FFFFFF in every browser. In numbers that is rgb(255, 255, 255) and hsl(0, 0%, 100%). Perceptually it is a very light, near-neutral color: OKLCH puts its lightness at 100% and its chroma at 0. It carries almost no chroma, so it behaves as a neutral rather than as a hue, and belongs with the off-whites.
White text only reaches 1:1 here, so black text is the safer pairing at 21:1. Because it is this light, White works best as a page or card background with dark text over it.
The closest CSS named colors to White, measured with CIEDE2000, are WhiteSmoke (#F5F5F5), Snow (#FFFAFA), GhostWhite (#F8F8FF). If White is not quite right, those are the nearest keywords to try before reaching for a custom value.
HEX
#FFFFFF
RGB
rgb(255, 255, 255)
HSL
hsl(0, 0%, 100%)
HWB
hwb(0 100% 0%)
CMYK
cmyk(0%, 0%, 0%, 0%)
LAB
lab(100 0 0)
LCH
lch(100 0 0)
OKLCH
oklch(100% 0 0)
WCAG asks for 4.5:1 between body text and its background. On #FFFFFF white text measures 1:1 and black text 21:1, so black clears it and white does not.
White text on White
WCAG 2.2
1:1
APCA
Lc 0
Fails AA body text
Fails AAA body text
Fails AA large text
Black text on White
WCAG 2.2
21:1
APCA
Lc 106
Passes AA body text
Passes AAA body text
Passes AA large text
Check White against any other color in the contrast checker.
White sits at 100% OKLCH lightness. Holding its hue and chroma and moving only that value carries it down to #060606, which keeps the family recognizable instead of letting it drift toward gray the way a plain HSL ramp does.
#C5C5C5
20% darker
#8E8E8E
40% darker
#5B5B5B
60% darker
#2D2D2D
80% darker
#060606
100% darker
Build a full accessible scale from #FFFFFF in the shade generator.
White barely moves under any of the four common forms of color blindness, the largest shift being 0 CIEDE2000 units under protanopia. It stays recognizable, though it still should not be the only thing carrying meaning.
Protanopia
#FFFFFF
Deuteranopia
#FFFFFF
Tritanopia
#FFFFFF
Achromatopsia
#FFFFFF
The nearest CSS keywords to #FFFFFF, ranked by perceptual distance rather than by how close their hex digits happen to look.