Panasonic PT-AE1000U - Screen Recommendations
For this Panasonic, considering its brightness, and it's very good black levels, I would think most buyers will be happiest with white surface screens, rather than gray. The extra lumens from a white screen with moderate gain (say 1.2 - 1.5) will be helpful for those who want to buy larger screens, and even if you go with a small screen, say 92" diagonal, the blacks will remain nice and dark.
I did almost all of the photo shoot on my 106" Carada Brilliant White, which claims 1.4 gain. I found the screen at that size to be a good match for movie viewing. By comparison, in my theater (viewing) room, I was projecting about 100" diagonal on my Stewart Firehawk, (a light gray high contrast surface), but still found the projector to be slightly underpowered.
In addition to the Carada, you can consider screens like Da-lite's Cinema Vision (gain 1.3), Stewart's StudioTek 130 (1.3 gain, and, I should note, considered by many to the the industry reference standard, but also more expensive). I'll also comment that with lower priced projectors I often find it hard to recommend a very expensive screen, unless the buyer is planning to upgrade projector quality. With a projector in the $4000 plus range, then spending for a top quality screen starts making real sense. There are a number of other screen manufacturers, of course, but those are the ones I am most familiar with.
If you really want a much larger screen, say over 110" diagonal, and your seating position is straight back from the screen, you can get a huge lumen boost by going to screens with over 2.0 gain. They will give you twice the brightness (or more) of a 1.0 gain, but the image brightness will roll off quickly as you move off to the sides. For example, a 2.0 gain 130" diagonal screen will have about the same brightness image as a 92" diagonal with a 1.0 gain screen.
As I mentioned earlier, the color performance was so good out of the box, in Cinema 1 mode, that, after measuring, all I adjusted was the brightness (-2), Contrast (+1), and Color (saturation), where I bounced back and forth between -2 and -3. (Mostly, I preferred -3).