Notification icons look bad on Nexus and Sony devices

I'm presenting different notifications in different scenarios in my application. Those notifications are created using the following code:

    protected void updateNotificationProgress() {
    notification.setContentTitle(notificationConfig.getTitle())
            .setContentText(String.format(getString(R.string.in_progress_formatted_string), (Utils.getUploadedFilesCount(this) + 1), Utils.getTotalUploadCount(this)))
            .setContentIntent(notificationConfig.getPendingIntent(this))
            .setSmallIcon(notificationConfig.getIconResourceID())
            .setProgress(Utils.getTotalUploadCount(this), Utils.getUploadedFilesCount(this), false)
            .setOngoing(true);

    startForeground(UPLOAD_NOTIFICATION_ID, notification.build());
}

While on most devices (LG G3, Samsung Galaxy devices) this notification looks as follows:

On Nexus devices this icon looks like this:

Why does this happen, and what is the proper way to fix this?