Belladonna on Dwarf Fortress
#220011 on #1d0200
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
1.01:1
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 0.0
Below Lc 15: the draft treats this as not text.
Too close to call.
Colour difference
ΔE00 6.8
clearly different
Between 5 and 10 — nobody would call these the same colour.
What the text colour has to become
#9b6a7f is the nearest colour of the same hue that passes AA on #1d0200, 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 1.01:1, ΔE00 7.2.
deuteranopia
Ratio 1.02:1, ΔE00 5.7.
tritanopia
Ratio 1.03:1, ΔE00 1.6.
The weakest of the three is tritanopia, where the two are ΔE00 1.6 apart against 6.8 for a trichromat — effectively one colour. If anything on your interface depends on telling these apart, it needs a second signal.
Both colours have pages of their own: Belladonna ·Dwarf Fortress · the same pair the other way round ·all pairs