Themes

  Themes are complete conversions for the look of a GUI.

  For example, one theme could use fancy 3D controls and another could use
  traditional, flat 2D controls.

  To create a theme, a custom GuiPainter needs to be created
  
Skins

  Skins are a specialty of the FlatGuiPainter and only modify the fonts and
  bitmap resources. Skins can be loaded from XML files and should be
  sufficient for most users in that they can completely alter the shape
  and design of any control.