Seafoam Slate

#a6bcbe

A neutral that has no useful hue — it reads as a grey. It is light — black text sits on it comfortably, white text does not.

Hex

#a6bcbe

RGB

166, 188, 190

OKLCh

77.9% 0.024 203.3°

CIELAB (D50)

74.6, -7.5, -3.7

What is true of this colour, and of no other

14 other named colours sit within ΔE00 2 of it — this part of the space is crowded, and the names here are finer distinctions than most people make.
It uses only 18% of the chroma available at this lightness and hue — there is a far more vivid version of this colour inside sRGB.
As text on white it measures APCA Lc 38.5; on black, Lc -63.9. The sign is the polarity, which the WCAG ratio discards.
Built into an eleven-step scale, 10 of the 10 adjacent pairs stay ΔE00 2 apart — see the ramp.
protanopia and deuteranopia and tritanopia shift it by ΔE00 9.8 and 10.6 and 20.0 — no red cone.

Text on this colour

White text

1.99:1 — fails AA

Black text

10.56:1 — passes AA

Black text is the better of the two at10.56:1. That is enough for body text.

As text on white, it needs to change

#667b7c is the nearest colour of the same hue that passes AA on white, at 4.50:1. Only the lightness moved.

Try it against your own background

The same colour, with one cone missing

As you see it

#a6bcbe

protanopia

#bababe · ΔE00 9.8

deuteranopia

#b6b6be · ΔE00 10.6

tritanopia

#b2b2f1 · ΔE00 20.0

Run a whole palette through all three

The twelve nearest named colours

Ranked by CIEDE2000 — perceptual distance, not hex arithmetic. The closest isOslo Blue at ΔE00 0.66: below 1.0 — an ordinary observer cannot tell these apart, even side by side. What the numbers mean.

Oslo BlueΔE00 0.66 · #a6bdbe
Grey GrainΔE00 0.801 · #a9bdbf
RainΔE00 1.279 · #abbebf
Alpine HazeΔE00 1.279 · #abbec0
Grey WoolΔE00 1.411 · #a9bbbc
Bleu ClairΔE00 1.445 · #aac0c4
Blue by YouΔE00 1.496 · #a0b7ba
Blue WillowΔE00 1.631 · #a8bbba
Windswept CloudsΔE00 1.848 · #9eb8bb
FalklandΔE00 1.877 · #a5bebd
Soft ShoreΔE00 1.911 · #a2bbc1
Dover SurfΔE00 1.963 · #aec3c4

12 of these have no page of their own: pages exist for the 4,961 colours the dataset marks as good names.