Oops, forgot the dust covers.

My experience yesterday when browsing online stores in China may shed some light on your first question. About the price impact with or without dust jacket：The Hobbit published by harpercollins in 2004, the price without dust jacket is almost only 20% of that with dust jacket.

Deagol wrote:

The paper colour is referred to as Silver Grey in the publisher's records.

Look at the jacket flaps for the unfaded colour - it often faded to white.

Just picked up this 3rd impression DJ Two Towers on a 4th impression book, I also have a 2nd '55 impression with no DJ but I don't have a 3rd impression book

The cover looks greyish white to the eye but I think it is more obvious on the inside and you can see the transition on the edge as deago says