While I took refraction off the table in #14 I'm putting it back on as it is pretty clear that refraction is partially responsible for what appears in OP's second photograph. The globular glass serves as a lens which images something dark (i.e. not the wall visible in the photo) onto the camera lens though the image is, obviously, not in focus. Hence the beer appears dark because he has photographed some part of the bathroom (probably the floor) which does not receive any light from the flash. Certainly it is not the image of the wall behind the glass because the beer is much darker and a different color from the wall.
At
http://www.pbase.com/image/136989737 I have posted a similar flash photograph which illustrates how this works. The white bar on the top simulates the foam on the beer which had collapsed by the time I realized how this works. That's there in order to force the camera to adjust gamma to fit the whole histogram between the rails just as it would do with real foam. The real foam is against the rail in OP's photo and the synthetic foam is against the rail in mine. As with the photos I posted yesterday I actually recorded a NEF and then had Photoshop do what a less sophisticated camera would do i.e. tweak gamma until both the darkest part of the picture and the "foam" fit between the A/D rails.
It is clear in my photo that the goblet is not imaging either the windows which nor the parts of the garage door panels behind it because both of those are lighter than the beer. Thus the bright light from the windows is refracted by the beer into some other part of the room. At the same time more feeble light from some dark part of the room is refracted by the beer so that it hits the camera lens. Changing the position of the camera so that it captures the window light obviously changes the brightness and color of the beer. This can be seen by pressing the "Next" button at pbase or going to
http://www.pbase.com/agamid/image/136990074. It is even possible to make out some details of the structure of the room image in this latter photo though I can't identify these objects i.e. I can't tell whether the lightest parts are the actual door lights or the patches of light cast by them onto the floor.
So it turns out refraction is very much a part of the explanation for the dark color of the beer in the glass. Note: This is the same 12.7 SRM beer as in the photos I posted yesterday.
Now of course it is also possible that OP's beer in the glass is in fact also darker or lighter than the beer in the carboy. We won't know whether that's the case if and until he puts up the picture I requested in an earlier post. But that would only be part of the story. As I said way back when here the color one sees (or the color that is recorded in a photograph) depends on the the thickness of beer through which the light passes, the coloring matter in the beer and the color quality of the light which passes through the beer. This latter is determined by whatever part of the surrounding room is imaged through the glass at the camera lens. Also, as stated way back when, any light scattered from yeast cells in the container, dew on the glass surface... will add to the transmitted light and add to the total light reaching the eye or camera. This will make beer with suspended yeast look lighter than it would when it is bright.
I doubt this will convince everyone but at least I am now satisfied that I fully understand what is going on here and may, thus, be better able to explain it.
