Customize Theme in UI

Can we add support to customize the theme in the UI like applying desktop backgrounds and colors? Or maybe add the ability to set backgrounds on the dashboards or under the different navigation pages. Seems like it would not be too hard to add the ability to set the background since you can do it on the users and the areas easily. Also the just like the areas have where you can upload and choose a image from the computer maybe add that ability to the picture entity buttons in the UI.