Document Theme Colors
Creates a color theme.
Name
Enter the name of the new theme.
Colors
For each of the theme named color, select the color in the color drop-down list.
LibreOffice creates 5 additional colors to the theme calculated from the main color. The calculations of the color variants are also hard coded in the theme and you cannot change them, only the main color.
Applied user defined theme is saved only in the document. To make it usable for other documents, use themes in document templates.