If you're just concerned about the external appearance of your GUI elements, I don't think there's any support for different UI elements than the ones provided. However, have you looked into a universal Theme
and style for your application?
Here are some excerpts from that document:
A style is a collection of properties that specify the look and format
for a View or window. A style can specify properties such as height,
padding, font color, font size, background color, and much more. A
style is defined in an XML resource that is separate from the XML that
specifies the layout.
A theme is a style applied to an entire Activity or application,
rather than an individual View (as in the example above). When a style
is applied as a theme, every View in the Activity or application will
apply each style property that it supports. For example, you can apply
the same CodeFont style as a theme for an Activity and then all text
inside that Activity will have green monospace font.
Here are some resources which talk about themes:
Let me know if that's what you wanted. Themes give you almost infinite possibilities to modify outwards appearance.