Create localized widget customizations. For example, change the background, foreground, and font colors. And have that customization only apply to the specific widget instance. It should also persist through out the related gadget. Meaning that if the Membership Application gadget page that is used for the widget creation has localized settings (content / layout etc. they should be reflected through all the gadget (and thus the widget) components.
You could use custom CSS on specific pages to customize appearance of widgets. Unlikely we will implement any widget specific customizations anytime soon