color contrast and readability between text and background colors

accessibility and appropriate background between brightness chart chromatic circle collection color colors colour combination complementary content contrast design difference enhanced eps8 foreground graphic guideline hex hexadecimal highlight hue large legibility luminance minimum multicolored natural ncs normal nuance opponent palette primary ratio readability requirement rgb sample saturation scheme secondary set shades small spectrum system text threshold tints tone value variation vector visibility visual wcag2 web wheel with