[celoyd]

Well-worn gray: https://en.wikipedia.org/wiki/Albedo

It’s a loose comparison, since both asphalt and the moon’s surface vary. Plus, there are tricky things like specular reflection and the opposition effect.

How can its color be compared to something on earth? Doesn't the (lack of) atmosphere have some effect?

You can hold a moon rock up against something on Earth. Or you can look at Earth and the moon from a distance with the same sensor, which is what Himawari-8 is doing.

The atmosphere does affect things: A huge plain of moon rocks on Earth’s surface would look bluer (hazier) than the moon would in the same picture from Himawari-8 (or an Apollo Hasselblad, etc.). And a moon rock in sunlight on Earth will look slightly yellower than one in the same light on the moon. But your eyes are constantly adapting to the surrounding illumination. Color perception is really complicated.