I have a PyShell, which is supposed to be derived from wx.stc.StyledTextCtrl. How do I change the color scheme that it currently uses?
You can use 
styledTextCtrl.StyleSetSpec(wx.stc.STC_STYLE_INDENTGUIDE, "fore:#CDCDCD")
(Bunch of .StyleSetSpec properties)
...
...
...
styCtrl.SetCaretForeground("BLUE")
styCtrl.SetSelBackground(True, wx.SystemSettings_GetColour(wx.SYS_COLOUR_HIGHLIGHT))
styCtrl.SetSelForeground(True, wx.SystemSettings_GetColour(wx.SYS_COLOUR_HIGHLIGHTTEXT))
...
(Bunch of Set*() commands)
Don't know if there is a way to load a pre-defined color scheme.
You could define it in YAML and load it up via the commands above and more.
wxPython: Changing the color scheme of a wx.stc.StyledTextCtrl