On 1bpp displays, ignore colour attributes. This makes pterm minimally useful

there, though (e.g.) switching to using reverse video for the cursor would
probably also help.  Displays with other silly depths (e.g. 2bpp) aren't
catered for, but I suspect they're rare in the X world.

[originally from svn r5696]

unix/gtkwin.c

@@ -1885,6 +1885,7 @@ void do_text_internal(Context ctx, int x, int y, wchar_t *text, int len,
     GdkGC *gc = dctx->gc;
     int ncombining, combining;
     int nfg, nbg, t, fontid, shadow, rlen, widefactor;
+    int monochrome = gtk_widget_get_visual(dctx->inst->area)->depth == 1;
 
     if (attr & TATTR_COMBINING) {
 	ncombining = len;
@@ -1892,8 +1893,8 @@ void do_text_internal(Context ctx, int x, int y, wchar_t *text, int len,
     } else
 	ncombining = 1;
 
-    nfg = ((attr & ATTR_FGMASK) >> ATTR_FGSHIFT);
-    nbg = ((attr & ATTR_BGMASK) >> ATTR_BGSHIFT);
+    nfg = ((monochrome ? ATTR_DEFFG : (attr & ATTR_FGMASK)) >> ATTR_FGSHIFT);
+    nbg = ((monochrome ? ATTR_DEFBG : (attr & ATTR_BGMASK)) >> ATTR_BGSHIFT);
     if (attr & ATTR_REVERSE) {
 	t = nfg;
 	nfg = nbg;