ContrastGraded by APCA, the Accessible Perceptual Contrast Algorithm, which measures how strongly text stands off its ground the way eyes see it, as lightness contrast (Lc) from 0 to about 106. Lc 60 and up reads as body text, 45 to 60 as large text and headlines; under 45, avoid it for text. The same measure picks black or white text everywhere on Chromary. The older WCAG 2 ratio is shown small under each for anyone quoting that standard.
Use
AaCharcoal on Electric SkyLc 53 · large textWCAG 2 · 7.4 : 1
AaClub Soda on Electric SkyLc 47 · large textWCAG 2 · 2.3 : 1
AaElectric Sky on CharcoalLc 51 · large textWCAG 2 · 7.4 : 1
Avoid
AaElectric Sky on Club SodaLc 42 · failsWCAG 2 · 2.3 : 1