Zenith marketed an optional protective soft felt bag for their high end Royal 500’s. Without the bag, many scratches would develop from the repeated sliding in and out of the leather cases. So these bags did a nice job of keeping the radio surface scratch free.
Zenith also issued a warning slip about the possible discoloration from storing radios in their leather carrying cases without the bag.
Perhaps that is why some of the white radios are now an ivory color? Just to be safe, I protect all of my finest radios in felt bags when they are not on display.
Below are some of the different styles of felt bags that I have been able to find.