God of Rain on Black Sabbath
#4466cc on #220022
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
3.68:1
Large text only
Not AAA (7:1). Swapping the two colours gives the same number — the ratio does not know which is the text.
APCA
Lc -25.4
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 39.5
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#5175dc is the nearest colour of the same hue that passes AA on #220022, 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 3.96:1, ΔE00 34.6.
deuteranopia
Ratio 3.54:1, ΔE00 33.4.
tritanopia
Ratio 3.47:1, ΔE00 50.4.
The weakest of the three is deuteranopia, where the two are ΔE00 33.4 apart against 39.5 for a trichromat — still clearly two colours.
Both colours have pages of their own: God of Rain ·Black Sabbath · the same pair the other way round ·all pairs