Overlay transparent background

[Leonid-Kiev]

Trying to implement layout as shown on the example
(1)if you like SwipeRefreshLayout drop-down refresh effect

However overlay is not transparent, but white!
How to change overlay color?
Here is the snippet of code:

<com.cjj.MaterialRefreshLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/refresh"
    app:overlay="true"
    app:wave_show="false"
    >
...
</com.cjj.MaterialRefreshLayout>