You will want to set the background of the imageButton to be something invisible. I do this by making the following XML drawable and setting it to the ImageButton's background. This will let the button still show a color when it is clicked, but blank otherwise.
blank_selector.xml
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_pressed="true" android:drawable="@color/some_color" />
<item android:drawable="@android:color/transparent" />
</selector>
<ImageButton
android:layout_width="62dp"
android:layout_weight="1"
android:layout_height="60dp"
android:id="@+id/im16"
android:layout_gravity="fill_horizontal"
android:src="@drawable/off1"
android:background="@drawable/blank_selector" />