Atlas Cedar on Opera
#5ca0a7 on #816575
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
1.74:1
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 -18.6
Clears Lc 15 — disabled or purely decorative text, which is not meant to be read.
Light text on a darker ground — the negative sign is the polarity.
Colour difference
ΔE00 42.8
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#c0f9ff is the nearest colour of the same hue that passes AA on #816575, at 4.50:1. Only the lightness moved, and some chroma was given up to stay inside sRGB — which is the point: your colour stays recognisably your colour.
And to someone missing a cone
protanopia
Ratio 1.96:1, ΔE00 18.6.
deuteranopia
Ratio 1.63:1, ΔE00 15.2.
tritanopia
Ratio 1.59:1, ΔE00 62.6.
The weakest of the three is deuteranopia, where the two are ΔE00 15.2 apart against 42.8 for a trichromat — still clearly two colours.
Both colours have pages of their own: Atlas Cedar ·Opera · the same pair the other way round ·all pairs