How can I rename highlight colours and add custom colours?
While viewing the Color Picker (Shift-Cmd-C), drag your custom colour from the large example bar at the top to a white box in the grid at the bottom (you may have to drag down the dot at the bottom of the palette to view the custom colour shelf). Colours added to the favourite swatches will appear in the drop-down menus for text and highlight colours. You can name the colours by switching to the “Color Palettes” view of the Color Picker (third icon from the left), choosing “Scrivener” from the Palette drop-down menu, dragging the colour into the list and double-clicking to rename it. You can rename the default highlight colours here as well.
