RGB vs HEX
How the two notations relate, converting by hand, shorthand and alpha, and when to use each.
RGB vs CMYK
Light versus ink, colour gamut, why the simple formula misleads, and a print workflow.
Colour theory
Hue, saturation and lightness, RGB and RYB wheels, harmony schemes and building a palette.
WCAG colour contrast
The contrast formula step by step, AA and AAA thresholds, large text and fixing failures.
Colour psychology
What research supports, where popular claims go too far, and how culture changes meaning.
Where to start
- If you are writing CSS or handing over a design, start with RGB vs HEX.
- If your work is going to print, read RGB vs CMYK before you send files to a printer.
- If you are choosing a palette, read colour theory, then check every text colour with the WCAG contrast guide.
- If someone tells you a colour will boost conversions, read colour psychology first.
Tools that go with the guides
Each guide links to the tool that puts it into practice: the colour picker for codes and palettes, the contrast checker for text and background pairs, the HEX/RGB converter for conversions with working, and the CSS colour names list.
The numbers in the guides' worked examples are calculated by the same code as the tools. See our editorial policy for how we check them.