display_manager ->colours_changed: Redraw all windows of all frames, including windows inside other windows
or devices such as tabs. Send this after changing colours in place, e.g.,
after changing the value of theme colours.
Before redrawing, each frame and each graphical in these frames whose
class defines display_manager->colours_changed
is sent this message. The built-in classes do not define it. An
application defines it if it holds colours that do not follow the theme
by themselves, e.g., images that are drawn
using image->draw_in
or colours that are computed from other colours:
colours_changed(W) :->
"Draw the icons again in the new colours"::
send(W, paint_icons).
