Es file explorer with the 3.0 update was made themeable. But no theming APIs were let out. There's only one first party theme available
Es classic :
Butttt... You can always modify this theme apk and make your own themes.
Like this gentleman has done here.
MIUI v5 theme for ES file explorer - Theme - MIUI Official Community - Mobile - http://en.miui.com/thread-14498-1-1.html
Be sure to do this.
I would like to see some material themes or whatever you guys want to make.
Let's make this happen.