GPS provides an extensive support for themes. Themes are predefined set of value for the preferences, for the key bindings, or any other configurable aspect of GPS.
For instance, color themes are a convenient way to change all colors in GPS at once, according to predefined choices (strongly contrasted colors, monochrome,...). It is also possible to have key themes, defining a set of key bindings to emulate e.g. other editors.
Any number of themes can be activated at the same time through the
preferences dialog (Edit->Preferences). This dialog contains a list
of all themes that GPS knows about, organized into categories for convenient
handling. Just click on the buttons on the left of each theme name to activate
that theme.
Note that this will immediately change the current preferences settings. For
instance, if the theme you just selected changes the colors in the editor,
these are changed immediately in the Editor->Fonts & Colors. You can
of course still press Cancel to keep your previous settings
If multiple themes are active at the same time and try to override the same preferences, the last theme which is loaded by GPS will override all previously loaded themes. However, there is no predefined order in which the themes are loaded.