Use theme-appropriate default colour in wxFontPickerCtrl

Don't hardcode black as the default font colour, as this can be
unreadable in dark mode.

Also update the unit test to not always expect the initial colour to be
black.

src/generic/fontpickerg.cpp

@@ -22,6 +22,10 @@
 
 #if wxUSE_FONTPICKERCTRL
 
+#ifndef WX_PRECOMP
+    #include "wx/settings.h"
+#endif // WX_PRECOMP
+
 #include "wx/fontpicker.h"
 
 #include "wx/fontdlg.h"
@@ -68,7 +72,7 @@ bool wxGenericFontButton::Create( wxWindow *parent, wxWindowID id,
 void wxGenericFontButton::InitFontData()
 {
     m_data.SetAllowSymbols(true);
-    m_data.SetColour(*wxBLACK);
+    m_data.SetColour(wxSystemSettings::GetColour(wxSYS_COLOUR_BTNTEXT));
     m_data.EnableEffects(true);
 }
 

tests/controls/pickertest.cpp

@@ -208,8 +208,7 @@ void FontPickerCtrlTestCase::ColourSelection()
 {
     wxColour selectedColour(0xFF4269UL);
 
-    CPPUNIT_ASSERT_EQUAL_MESSAGE("Default font picker color must be black",
-        m_font->GetSelectedColour(), wxColour(*wxBLACK));
+    CHECK( m_font->GetSelectedColour() != selectedColour );
 
     m_font->SetSelectedColour(selectedColour);