Android Notification is not showing Colour Icon in Marshmallow

First : Its not from Marshmallow, Notification icon started turning out WHITE from Lollipop itself.

Checkout http://developer.android.com/design/style/iconography.html you will see that the white style is how notifications are meant to be displayed in Android Lollipop.

In Android Lollipop, Google also suggests you to use a color that will be displayed behind the (white) notification icon - https://developer.android.com/about/versions/android-5.0-changes.html

Second : Solution to this is setting LargeIcon to Notification Builder

Bitmap largeIcon = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);

NotificationCompat.Builder builder = new NotificationCompat.Builder(context)
                .setSmallIcon(R.drawable.ic_launcher)
                .setLargeIcon(largeIcon)
                .setContentText(data)
                .setContentTitle("Notification from Parse")
                .setContentIntent(pendingIntent);

then, your Notification will look something like this :

You can also set the color to background of Notification Icon by using .setColor().