Thanks for the replies.
The leaves look even greyer in person, so I thought about mold, but they don't look furry. Also, we don't have (much) humidity here in the northern San Joaquin Valley in California. We just don't have the attendant problems that exist in other parts of the country. I also thought about mites because of the way the leaves are curling, but I didn't see any evidence of webs. They have a small Mandarin tree in that bed that, they say, may be showing similar signs. I was looking at it yesterdy and what I saw on the tree was iron deficiency but I didn't look that closely.
It's probably too late to buy new tomato plants here so they're going to try to save these.
After looking at some online pictures I suspect it might just be really poor soil:
http://customers.hbci.com/~wenonah/min-def/tomatoes.htm
http://www.haifa-group.com/knowledge...ency_symptoms/
http://www.oliviassolutions.com/blog...ies-in-plants/