Changing the "theme" in Enthought Traits UI with Qt as the backend

I'm currently writing code for a customer using Enthought Traits, and in particular Traits UI. Traits as a whole is a very nice toolkit for use in scientific programming, but you can find out about that by googling in the normal manner.

The specific issue, though, is  that we've moved to using pyside/Qt4 as the GUI backend, instead of wx(Python) - enabled, for instance, by doing:

    try:
        from traits.etsconfig.api import ETSConfig
        ETSConfig.toolkit = 'qt4'
    except ValueError:
        pass

Some things are done a little bit differently with the Qt backend, though, and it's not always obvious how. In particular, traits UI has always allowed "theming", and the normal way to do this with the traditional wx backend is using something like:

    from traitsui.api import Theme
    ...
    Item('move_to_loading_area_btn', item_theme=Theme('@std:BE5')),

 (note that this is not the syntax for the item_theme argument shown in the documentation, that doesn't seem to work - so this is also "a useful reference").

This doesn't work with the Qt backend. It turns out that the way to do it is to specify a Qt stylesheet, which can be done as a string:

    Item('move_to_loading_area_btn', style_sheet='* { color: red }'),

Useful Qt references are then:

• http://qt-project.org/doc/qt-4.8/stylesheet-syntax.html
• http://qt-project.org/doc/qt-4.8/stylesheet-reference.html#list-of-properties
• http://qt-project.org/doc/qt-4.8/stylesheet-examples.html

(blogged here because no-one else seems to have described doing this)