The reason why people don't use ChessGUI is that it offers only 1 percent of what Winboard or Arena offers.
ChessGUI does not even analyze games and knows nothing about the internet.
Colours of pieces, board, and other GUI elements can be easily changed.
However, the Wood/Marble stuff is missing.
ChessGUI 0.173 solves Testsuites, if engines are marked as able to analyze.
Help file is scanty and not up-to-date, so if you have questions, ask Graham.

ChessGUI is still very unstable if mouse button is held pressed, especially
between games. This instability means engine/GUI communication stops.
If you like the Windows Mine Sweeper game, you'll also like ChessGUI.
It's all about mine fields.
Matthias.