Made holding ctrl and clicking on an overlay rectangle set the color to the

default value as well as the label to the default.

dlib/gui_widgets/widgets.cpp

@@ -6592,6 +6592,7 @@ namespace dlib
             if (best_dist < 13)
             {
                 overlay_rects[best_idx].label = default_rect_label;
+                overlay_rects[best_idx].color = default_rect_color;
                 highlighted_rect = best_idx;
                 highlight_timer.stop();
                 highlight_timer.start();

dlib/gui_widgets/widgets_abstract.h

@@ -2351,8 +2351,9 @@ namespace dlib
                 on the part.  If you want to move any rectangle or an object part then
                 shift+right click and drag it.
                 
-                Finally, if you hold Ctrl and left click an overlay rectangle it will 
-                change its label to get_default_overlay_rect_label().
+                Finally, if you hold Ctrl and left click an overlay rectangle it will
+                change its label to get_default_overlay_rect_label() and color to
+                get_default_overlay_rect_color().
 
                 The image is drawn such that:
                     - the pixel img[0][0] is the upper left corner of the image.