Inspect SeaShell (#FFF5EE) in HEX, RGB, HSL, LCH and OKLCH, check its contrast, and copy the value you need.
SeaShell
#FFF5EE
Black text reads best on this background, at 19.55:1.
SeaShell is one of the 148 CSS named colors, and resolves to #FFF5EE in every browser. In numbers that is rgb(255, 245, 238) and hsl(25, 100%, 97%). Perceptually it is a very light, near-neutral color: OKLCH puts its lightness at 98% and its chroma at 0.014. 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 1.07:1 here, so black text is the safer pairing at 19.55:1. Because it is this light, SeaShell works best as a page or card background with dark text over it.
The closest CSS named colors to SeaShell, measured with CIEDE2000, are Linen (#FAF0E6), FloralWhite (#FFFAF0), Snow (#FFFAFA). If SeaShell is not quite right, those are the nearest keywords to try before reaching for a custom value.
HEX
#FFF5EE
RGB
rgb(255, 245, 238)
HSL
hsl(25, 100%, 97%)
HWB
hwb(25 93% 0%)
CMYK
cmyk(0%, 4%, 7%, 0%)
LAB
lab(97.18 2.59 4.64)
LCH
lch(97.18 5.31 60.82)
OKLCH
oklch(97.6% 0.0143 57.59)
WCAG asks for 4.5:1 between body text and its background. On #FFF5EE white text measures 1.07:1 and black text 19.55:1, so black clears it and white does not.
White text on SeaShell
WCAG 2.2
1.07:1
APCA
Lc 0
Fails AA body text
Fails AAA body text
Fails AA large text
Black text on SeaShell
WCAG 2.2
19.55:1
APCA
Lc 101
Passes AA body text
Passes AAA body text
Passes AA large text
Check SeaShell against any other color in the contrast checker.
SeaShell sits at 98% OKLCH lightness. Holding its hue and chroma and moving only that value carries it down to #090502, which keeps the family recognizable instead of letting it drift toward gray the way a plain HSL ramp does.
#C7BDB6
20% darker
#918882
40% darker
#5F5751
60% darker
#312A25
80% darker
#090502
100% darker
Build a full accessible scale from #FFF5EE in the shade generator.
The biggest shift is under achromatopsia, where #FFF5EE reads as #F7F7F7, 5 CIEDE2000 units away. If SeaShell is the only thing marking a state or a series, roughly one viewer in twelve will miss it.
Protanopia
#F8F5EE
Deuteranopia
#FAF7EE
Tritanopia
#FFF3F3
Achromatopsia
#F7F7F7
The nearest CSS keywords to #FFF5EE, ranked by perceptual distance rather than by how close their hex digits happen to look.