How to modify button colors

Here's one of the button's axml:

 <Button
            android:text="1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight=".25"
            android:id="@+id/btn1" />

This button is light gray

Here's another button:

 <Button
            android:text="-"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@+id/btn6"
            android:layout_alignTop="@+id/btn6"
            android:layout_weight=".25"
            android:background="#F9E79F"
            android:id="@+id/btnSub" />

and this is yellow (goldenrod?)?

And here's how it looks:

How do I get the yellow buttons to be like the light gray ones? That is, bounded by white?

RON