jeremy I think you are correct, but every now and then one just seems to work in color like the one below.

Neil
Reminds me of somebody I almost bumped into at the supermarket this morning, which just serves to shows you the trouble with self-tailored masks.
(I also tried to buy one of those ubiquitous little bottles of 98% alcohol that are usually on sale. Couldn't see a single one and so I approached a young lady in store uniform and asked her where they were shelved. Her big eyes gazed at me over her mask as if I were an idiot straight off the aeroplane: but señor, we have none - they were all sold out weeks ago!
Oh well...)
Rob