I look out and observe that the sky is a flat, pale, dirty blue. As I was about to remark that "The sky is a flat, pale dirty blue," I consider that there really is no sky. What we call "sky" is an imaginary field superimposed on the atmosphere as viewed from the earth's surface . It's an illusionary perception of color and form effected by reflected and refracted light, defined differently by observers from their respective perspectives.
So I might as well say "The sky is a vibrant pink with flaming orange stripes," or "The sky is scumbled with a neon lightshow," or "The sky is the blue-black of the deep sea, accentuated with crushed pearlescent shell," -- because I'm sure it is true, as viewed from some other latitude or longitude. It's still much more romantic than saying"The sky is a flat, pale, dirty blue," though that is what I perceive right now.