ACCESSIBLE COLORS DON'T EXIST

Summary from the TLDR Design newsletter

No single color can be accessible, because contrast is a property of two colors together rather than of one. WCAG asks for 4.5:1 on regular text and 3:1 on large text and UI components, so a bright yellow fails on white yet works on dark. Brands should hand designers a palette of pre-approved color combinations with sufficient contrast instead of chasing an accessible color.