Acoustic Brown on Atlas Cedar
#766b69 on #5ca0a7
Body text at this size
And the smaller size most interfaces actually use for paragraphs — the size that decides whether a pair is usable.
Caption text, which almost nothing passes.
WCAG 2.1
1.73:1
Fails AA
Not AAA (7:1). Swapping the two colours gives the same number — the ratio does not know which is the text.
APCA
Lc 17.2
Clears Lc 15 — disabled or purely decorative text, which is not meant to be read.
Dark text on a lighter ground.
Colour difference
ΔE00 30.4
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#362d2b is the nearest colour of the same hue that passes AA on #5ca0a7, at 4.50:1. Only the lightness moved — which is the point: your colour stays recognisably your colour.
And to someone missing a cone
protanopia
Ratio 1.89:1, ΔE00 19.3.
deuteranopia
Ratio 1.64:1, ΔE00 19.8.
tritanopia
Ratio 1.64:1, ΔE00 55.3.
The weakest of the three is protanopia, where the two are ΔE00 19.3 apart against 30.4 for a trichromat — still clearly two colours.
Both colours have pages of their own: Acoustic Brown ·Atlas Cedar · the same pair the other way round ·all pairs