I never tried custom colouring the window from a script (only done it by xml) so I can't give you an answer for that.
As for slider controls, in fact you can get the value by sending a TBM_GETPOS message to the control handle. You can also set the value on the slider control by sending TBM_SETPOS with a value as a parameter
code:
PlusWnd.SendControlMessage("SliderControl", 0x405 /* TBM_SETPOS */, 1, 255 /* new value */);
PlusWnd.SendControlMessage("SliderControl", 0x400 /* TBM_GETPOS */, 0, 0);
TBM_SETPOS = TBM_GETPOS+5