Move the bottom padding from the shape
to the parent item
:
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item>
<bitmap android:src="@drawable/img1" />
</item>
<item android:bottom="20dp">
<shape android:shape="rectangle" >
<solid android:color="@color/color1" />
</shape>
</item>
</layer-list>
See http://idunnolol.com/android/drawables.html#layer-list for more info.