How do you add custom color to Tableau?

For a single colour, open the colour legend, click Edit Colors, select the data item, choose More Colors and enter a hex value.

For a palette you want available everywhere, edit Preferences.tps in My Tableau Repository. Add a palette element with a name, a type, and a list of hex colours, then restart Desktop. The palette then appears in the Edit Colors dropdown in every workbook.

Palette types are `regular` for categorical, `ordered-sequential` for a single-hue ramp, and `ordered-diverging` for a two-ended one.

The reason to bother with the .tps route is consistency — brand colours defined once, used identically across every workbook, rather than someone approximating them by eye each time.