Inspect Turquoise (#40E0D0) in HEX, RGB, HSL, LCH and OKLCH, check its contrast, and copy the value you need.
Turquoise
#40E0D0
Black text reads best on this background, at 12.79:1.
Turquoise is one of the 148 CSS named colors, and resolves to #40E0D0 in every browser. In numbers that is rgb(64, 224, 208) and hsl(174, 72%, 56%). Perceptually it is a light, moderately saturated color: OKLCH puts its lightness at 82% and its chroma at 0.131. It sits in the cyans at 185 degrees of OKLCH hue, and reads as a cool color.
White text only reaches 1.64:1 here, so black text is the safer pairing at 12.79:1. That combination of lightness and chroma makes it a workable mid-tone, the kind of value that lands in the middle of a shade scale.
The closest CSS named colors to Turquoise, measured with CIEDE2000, are MediumTurquoise (#48D1CC), DarkTurquoise (#00CED1), Aqua (#00FFFF). If Turquoise is not quite right, those are the nearest keywords to try before reaching for a custom value.
HEX
#40E0D0
RGB
rgb(64, 224, 208)
HSL
hsl(174, 72%, 56%)
HWB
hwb(174 25% 12%)
CMYK
cmyk(71%, 0%, 7%, 12%)
LAB
lab(80.96 -45.14 -4.68)
LCH
lch(80.96 45.38 185.92)
OKLCH
oklch(82.23% 0.1307 185.09)
WCAG asks for 4.5:1 between body text and its background. On #40E0D0 white text measures 1.64:1 and black text 12.79:1, so black clears it and white does not.
White text on Turquoise
WCAG 2.2
1.64:1
APCA
Lc 31
Fails AA body text
Fails AAA body text
Fails AA large text
Black text on Turquoise
WCAG 2.2
12.79:1
APCA
Lc 75
Passes AA body text
Passes AAA body text
Passes AA large text
Check Turquoise against any other color in the contrast checker.
Turquoise sits at 82% OKLCH lightness. Holding its hue and chroma and moving only that value carries it up to #E5FFFB and down to #000807, which keeps the family recognizable instead of letting it drift toward gray the way a plain HSL ramp does.
#4FEBDA
20% lighter
#5CF5E5
40% lighter
#6FFFEF
60% lighter
#B5FFF4
80% lighter
#E5FFFB
100% lighter
#00B0A3
20% darker
#008176
40% darker
#00544D
60% darker
#002B27
80% darker
#000807
100% darker
Build a full accessible scale from #40E0D0 in the shade generator.
Hues rotated around #40E0D0 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.
Turquoise sits at 185 degrees. Rotating it a half turn lands on 5 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 Turquoise at 155 and 215 degrees. They stay close enough to read as the same family, which is what you want for hover states, secondary surfaces and gradients.
185, 305 and 65 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 5 degrees, this pair flanks it at 335 and 35. You keep most of the contrast of a complementary pairing while losing the harshness.
Explore more combinations around Turquoise on the color wheel.
The biggest shift is under deuteranopia, where #40E0D0 reads as #A9B2D2, 28.5 CIEDE2000 units away. If Turquoise is the only thing marking a state or a series, roughly one viewer in twelve will miss it.
Protanopia
#CBCCD0
Deuteranopia
#A9B2D2
Tritanopia
#1AEADA
Achromatopsia
#BDBDBD
The nearest CSS keywords to #40E0D0, ranked by perceptual distance rather than by how close their hex digits happen to look.