Your color as a brand: the primary, the secondary colors from the chosen scheme, lighter and darker versions for backgrounds and states, and the neutrals from night to paper through greys tinted with your hue. Copy it as CSS.
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 WatermelonLc 50 · large textWCAG 2 · 6.9 : 1
AaMilk on WatermelonLc 50 · large textWCAG 2 · 2.5 : 1
AaWatermelon on CharcoalLc 48 · large textWCAG 2 · 6.9 : 1
AaWatermelon on MilkLc 45 · large textWCAG 2 · 2.5 : 1