[android] How do I change Android Studio editor's background color?

You can change it by going File => Settings (Shortcut CTRL+ ALT+ S) , from Left panel Choose Appearance , Now from Right Panel choose theme.

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Android Studio 2.1

Preference -> Search for Appearance -> UI options , Click on DropDown Theme

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Android 2.2

Android studio -> File -> Settings -> Appearance & Behavior -> Look for UI Options

EDIT :

Import External Themes

You can download custom theme from this website. Choose your theme, download it. To set theme Go to Android studio -> File -> Import Settings -> Choose the .jar file downloaded.