I thought of replying to this thread, but the forum tells me it's rather old. Also, it's about the Sony model. (AFAIK, they use the same screen tech, but why not use a forum that's about the same hardware I'm using :-)

Anyway.
When it's cold, the screen/ink starts to fade after a while, with every new refresh there is less black. I haven't (yet?) found out if it disappears altogether.

Once in the warm, it seems to "thaw" for a while (color getting stronger), then work as usual.

The temperature should be well within the storage temperatures - but how about actually using it when it's close to or even below zero (Celsius)?
Could that somehow damage the display?
I have not had the ink fade out during cold weather. Of course I have not used my Cool-er outside in cold weather. I tend to read inside.

Sorry that I don't have any more info for you.

Amy
I have had an ink display problem, but only once... and it was quite cold outside and inside, but I don't know if that caused the problem.

One morning, when I turned on the Cool-er, the pages start up page appeared blurred but readable. The next screen was more blurred, and by the time I navigated to the ebook I was reading, the page was just covered in undecipherable squiggles.

I reset the cool-er, which didn't work. I then assumed it was a major problem and just turned it off and put it away. A couple of hours later I turned it back on, and the problem had gone away...

regards,
It's known that e-ink screens, generally, are sensitive to extreme temperatures. Cold weather causes kind of bleaching up! If your reader gets out of the cold, things should be back to normal pretty soon again! So don't worry! This is REALLY harmless!
I have the same thing, having been using my reader in the sub-Arctic temperatures we've been having in the UK lately. It doesn't seem to do any harm.

For other in this thread - it happens when the ambient temperature around the COOL-ER is really, really cold, i.e. less than zero degrees Celsius. If it's cold outside and you're snug and warm inside you won't see these symptoms.
Seriously who reads their ebooks outside in subzero temperatures??


Amy
I've used my ebook readers in the car with a recorded car temp of -1 and they worked fine - luckily the car soon started to heat up.

When traveling, we're not always lucky to be in the warm. Waiting around at bus / coach / train stations can be cold (especially where there is no indoor waiting room) and in these situations I'd prefer to read than sit doing nothing. So it happens, personally I'd prefer to read in the warm but not always so!
Well, it's all the fault of the local train company - they refuse to heat unenclosed waiting areas, just because it'd be a bit inefficient to do so...

But seriously, it's winter right now, even some snow, and I usually have to wait a few minutes in the open air till my train arrives. I don't mind the cold air, but I like to read - because after a while the walls are boring to look at.
I took it two days ago, had to let the dog out and i was in the middle of a chapter. Noticed the same thing, characters were fading there was some extra grey lines in the middle of the screen.
Same here. I read a lot while walking from site to site at work, and the subzero temperatures meant my cool-er's screen was a bit fadey and fraggy-looking. Warmed up fine.