Black Box on Intrigue Red
#0f282f on #b24648
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
2.83:1
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 23.8
Clears Lc 15 — disabled or purely decorative text, which is not meant to be read.
Dark text on a lighter ground.
Colour difference
ΔE00 44.9
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#d1eff8 is the nearest colour of the same hue that passes AA on #b24648, 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 2.17:1, ΔE00 23.0.
deuteranopia
Ratio 3.20:1, ΔE00 38.0.
tritanopia
Ratio 4.17:1, ΔE00 62.6.
The weakest of the three is protanopia, where the two are ΔE00 23.0 apart against 44.9 for a trichromat — still clearly two colours.
Both colours have pages of their own: Black Box ·Intrigue Red · the same pair the other way round ·all pairs