Olympian Blue on Purple Climax
#1c4c8c 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
1.42:1
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 9.6
Below Lc 15: the draft treats this as not text.
Dark text on a lighter ground.
Colour difference
ΔE00 24.1
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#cbe1ff is the nearest colour of the same hue that passes AA on #8800ff, at 4.50:1. Only the lightness moved, and some chroma was given up to stay inside sRGB — which is the point: your colour stays recognisably your colour.
And to someone missing a cone
protanopia
Ratio 1.14:1, ΔE00 14.5.
deuteranopia
Ratio 1.58:1, ΔE00 14.8.
tritanopia
Ratio 1.49:1, ΔE00 16.3.
The weakest of the three is protanopia, where the two are ΔE00 14.5 apart against 24.1 for a trichromat — still clearly two colours.
Both colours have pages of their own: Olympian Blue ·Purple Climax · the same pair the other way round ·all pairs