CardView background color always white

If you want to change the card background color, use:

app:cardBackgroundColor="@somecolor"

like this:

<android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:cardBackgroundColor="@color/white">

</android.support.v7.widget.CardView>

Edit:
As pointed by @imposible, you need to include

xmlns:app="http://schemas.android.com/apk/res-auto"

in your root XML tag in order to make this snippet function