title: Push notification white square icon
body: <p>I'm using pushwoosh for push notification service.
  according to the Android documentation I've used a white icon for notification.
  but on some devices, I see white square again. </p>
  
  <p>on other hand,s I've used a colored icon and I see the colored notification.
  why on some devices I can use a colored icon, and on other, I always see the white icon?</p>