I teach painting and many of the points I make in class are covered by this resource. Importantly, that the sky is almost always the brightnest thing in a landscape, even at night and that colour vision at night is poor. Great resource.
The sky is bright against the landscape if you're far enough away from civilization. In an urban environment, the night sky is black with some stars at best, blue or pink at worst, and spots of artificial light overpower it here and there. Even really far away, in complete darkness, with the sky literally covered by a million stars, the sky mostly remains pitch black to the naked eye, with very faint bits of color fr…
See Orion's belt? Pretend that's a straight line. Now look perpendicular to it in both directions and you come to some fairly bright stars about the same distance both ways. One of those is red/orange and the other is blue/green. Visible to the naked eye even in an urban setting.