Android button with different background colors

As your error states, you have to define drawable attibute for the items (for some reason it is required when it comes to background definitions), so:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true" android:drawable="@color/red"/> <!-- pressed -->
    <item android:state_focused="true" android:drawable="@color/blue"/> <!-- focused -->
    <item android:drawable="@color/black"/> <!-- default -->
</selector>

Also note that drawable attribute doesn’t accept raw color values, so you have to define the colors as resources. Create colors.xml file at res/values folder:

<?xml version="1.0" encoding="utf-8"?>
<resources>
     <color name="black">#000</color>
     <color name="blue">#00f</color>
     <color name="red">#f00</color>
</resources>