Why does the Moon appear gray when passing between the Sun and the Earth? Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth?



The photo was taken by DSCOVR at Lagrange point 1.

In the picture, The Moon appears dark gray. Of course the Earth appears bright, reflecting sunlight from clouds and water. The Moon's surface is gray and should reflect less light than the Earth.

It should be irrelevant that we see the far side, since the reflectivity of the Moon's surface should be the same on the far side as the side that faces the Earth.

The midnight full Moon appears much, much brighter as seen from Earth than it does in this picture, despite the fact that the amount of sunlight reflecting from the surface of the Moon is the same in both instances.

I understand the photo was taken with 3 separate exposures of red, blue and green, but this should not affect the brightness.

So why does it appear so dull?
That's what it really would look like if you were there with DSCOVR. The albedo of the Moon is only about 0.136, about half of the Earth's average albedo. Of course the part with clouds is higher.

I was shocked too, but it was explained in written copy that accompanied  the release of the original image. 


  Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth?


It does. If the moon were a diffuse, white ball, a full moon would be about seven times brighter!

If you watch the image or GIF, the Moon is roughly the same brightness as central Australia or the Sahara region.

Phil Plait explains well in Bad Astronomy.

There's a lot to read here.

EDIT: I just ran across these images of astronauts on the surface while reading this answer. Their suits are not 100% white to begin with, but the Lunar soil - at least in these locations - is significantly darker. It is close to the same color as the (presumably) nearly-black radiator fins for the heat sink of the RTG unit (2nd photo) at the astronaut's foot. 



above: "Buzz Aldrin carries the EASEP." from here



above: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here.



above: Image from NASA/NOAA from Bad Astronomy