Yes, there are skins available for this browser, but unfortunately, there is no store to download them from, like you would normally do on Chrome or Firefox. The skins need to be downloaded from the Forum posts created by users. Luckily, there is a simple way to browse the skins.
Forums Skins: http://forum.maxthon.com/index.php/tags/forums/Skin/
Download the mxskin file and double click it, and the browser will install it. To switch the newly installed skin, go to UI - Main menu > Skins.