The "compare and contrast" reminded me of an exercise we are doing right now. The site is in German. It basically says, the test users as documented on its front page can chose their own themes from the given list. If the user wants to swap themes quickly appending &theme=THEMENAME to the URL will do the trick.
MoodleCloud plans include the Moodle Standard Theme and the Boost Theme.
Installing your own theme is not possible on MoodleCloud, however you are able to customise many aspects of the themes we have available. This includes the colours, logos, css styles etc.