Cover of Night on Purple Climax
#494e4f on #8800ff
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
1.40:1
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 9.8
Below Lc 15: the draft treats this as not text.
Dark text on a lighter ground.
Colour difference
ΔE00 24.9
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#dae0e1 is the nearest colour of the same hue that passes AA on #8800ff, 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 1.18:1, ΔE00 30.7.
deuteranopia
Ratio 1.52:1, ΔE00 30.1.
tritanopia
Ratio 1.46:1, ΔE00 11.9.
The weakest of the three is tritanopia, where the two are ΔE00 11.9 apart against 24.9 for a trichromat — still clearly two colours.
Both colours have pages of their own: Cover of Night ·Purple Climax · the same pair the other way round ·all pairs