Out of the Blue on Olympian Blue
#1199ee on #1c4c8c
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
2.77:1
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 -30.3
Clears Lc 30 — the floor: below this the draft considers text not readable at any size.
Light text on a darker ground — the negative sign is the polarity.
Colour difference
ΔE00 29.1
different colours
Above 10 — related only in the sense that both are colours.
What the text colour has to become
#7bc3ff is the nearest colour of the same hue that passes AA on #1c4c8c, 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 2.89:1, ΔE00 29.7.
deuteranopia
Ratio 2.70:1, ΔE00 26.3.
tritanopia
Ratio 2.26:1, ΔE00 20.6.
The weakest of the three is tritanopia, where the two are ΔE00 20.6 apart against 29.1 for a trichromat — still clearly two colours.
Both colours have pages of their own: Out of the Blue ·Olympian Blue · the same pair the other way round ·all pairs