Cover of Night on Belladonna
#494e4f on #220011
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
2.31:1
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 -12.5
Below Lc 15: the draft treats this as not text.
Light text on a darker ground — the negative sign is the polarity.
Colour difference
ΔE00 27.6
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#757a7b is the nearest colour of the same hue that passes AA on #220011, 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 2.41:1, ΔE00 21.3.
deuteranopia
Ratio 2.26:1, ΔE00 19.3.
tritanopia
Ratio 2.16:1, ΔE00 25.8.
The weakest of the three is deuteranopia, where the two are ΔE00 19.3 apart against 27.6 for a trichromat — still clearly two colours.
Both colours have pages of their own: Cover of Night ·Belladonna · the same pair the other way round ·all pairs