When drawing text using the dc and gc wxWidgets driver it always uses cmap0 colours. Setting the foreground colour using cmap1 has no effect upon the text colour. I think from looking at the code (but I have not checked) that the agg wxWidgets text colour can be set by either cmap0 or cmap1. I've checked the psc driver and this allows setting the colour using cmap1. This behaviour is not documented in the manual as far as I can see.
This can be fixed by editing the wxPLDevDC::ProcessString function in wxwidgets_dc.cpp and wxwidgets_gc.cpp - the appropriate lines are pretty obvious.
I'm sorry I can't submit a patch but I only have access to a windows machine so don't have access to diff, which I think is needed for creating patches