Inspect Azure (#F0FFFF) in HEX, RGB, HSL, LCH and OKLCH, check its contrast, and copy the value you need.
Azure
#F0FFFF
Black text reads best on this background, at 20.45:1.
Azure is one of the 148 CSS named colors, and resolves to #F0FFFF in every browser. In numbers that is rgb(240, 255, 255) and hsl(180, 100%, 97%). Perceptually it is a very light, near-neutral color: OKLCH puts its lightness at 99% and its chroma at 0.016. 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 1.03:1 here, so black text is the safer pairing at 20.45:1. Because it is this light, Azure works best as a page or card background with dark text over it.
The closest CSS named colors to Azure, measured with CIEDE2000, are MintCream (#F5FFFA), LightCyan (#E0FFFF), AliceBlue (#F0F8FF). If Azure is not quite right, those are the nearest keywords to try before reaching for a custom value.
HEX
#F0FFFF
RGB
rgb(240, 255, 255)
HSL
hsl(180, 100%, 97%)
HWB
hwb(180 94% 0%)
CMYK
cmyk(6%, 0%, 0%, 0%)
LAB
lab(98.88 -5.07 -1.78)
LCH
lch(98.88 5.38 199.35)
OKLCH
oklch(98.9% 0.0157 196.9)
WCAG asks for 4.5:1 between body text and its background. On #F0FFFF white text measures 1.03:1 and black text 20.45:1, so black clears it and white does not.
White text on Azure
WCAG 2.2
1.03:1
APCA
Lc 0
Fails AA body text
Fails AAA body text
Fails AA large text
Black text on Azure
WCAG 2.2
20.45:1
APCA
Lc 104
Passes AA body text
Passes AAA body text
Passes AA large text
Check Azure against any other color in the contrast checker.
Azure sits at 99% OKLCH lightness. Holding its hue and chroma and moving only that value carries it down to #010707, which keeps the family recognizable instead of letting it drift toward gray the way a plain HSL ramp does.
#B8C6C6
20% darker
#829090
40% darker
#505D5D
60% darker
#232F2F
80% darker
#010707
100% darker
Build a full accessible scale from #F0FFFF in the shade generator.
The biggest shift is under protanopia, where #F0FFFF reads as #FDFDFF, 6.8 CIEDE2000 units away. If Azure is the only thing marking a state or a series, roughly one viewer in twelve will miss it.
Protanopia
#FDFDFF
Deuteranopia
#F9FBFF
Tritanopia
#ECFFFF
Achromatopsia
#FCFCFC
The nearest CSS keywords to #F0FFFF, ranked by perceptual distance rather than by how close their hex digits happen to look.