Master Chief on Atlas Cedar
#507d2a on #5ca0a7
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
1.63:1
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 15.3
Clears Lc 15 — disabled or purely decorative text, which is not meant to be read.
Dark text on a lighter ground.
Colour difference
ΔE00 31.3
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#1b3600 is the nearest colour of the same hue that passes AA on #5ca0a7, 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 1.65:1, ΔE00 32.8.
deuteranopia
Ratio 1.62:1, ΔE00 36.6.
tritanopia
Ratio 1.59:1, ΔE00 15.0.
The weakest of the three is tritanopia, where the two are ΔE00 15.0 apart against 31.3 for a trichromat — still clearly two colours.
Both colours have pages of their own: Master Chief ·Atlas Cedar · the same pair the other way round ·all pairs