aracter string specifying the color theme to be used. Possible options are <code>'standard'</code>, <code>'catalog'</code>, <code>'metro'</code>, <code>'pastel'</code>, <code>'beach'</code>, <code>'moonlight'</code>, <code>'goo'</code>, or <code>'sunset'</code>. Note that this option supports fitted objects with three chains. If the object was fitted using a different number of chains then the colors are either automatically chosen, or can be specified by the user via the argument <code>custom_theme</code>.