A Google search says yes, since it pointed me to this:
http://bootsnipp.com/snippets/featur...pdown-menu-bs3
The theme changer dropdown is dynamically appended to the end of the navigation menu with javascript in
themeswitcher-kyt.js. You would need to add the css from the link above to your stylesheet and then manually modify line 12, which won't be easy, for three reasons:
1) It has to stay on one line or the read out of it will break.
2) Slashes in closing tags must be backslashed.
3) Quotes must be backslashed.
Then you need to follow the instructions in the commented out are half way through the file. Basically, the links to themes are not true links, since javascript needs to be used to swap out the css files. Add a custom class to the theme you added to the list, then copy and paste out the code provided in the commented section of the file to below it so it's no longer in the comment zone, and make sure the class name from the list and the snippet of code that will swap out the css when clicked are the same.
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disclaimer: This is really something only meant for developers who know what they're doing and the theme changer should honestly be removed from any active, published website. If you just want to see what a different set of colors look like, I really recommend just changing what file you're linking to in your theme's header.