Have you ever asked yourself why those photoless days – the cloudy ones, are so diffused and blue?” Probably not, because it seems to not be an important question to ask yourself. Unless you’re me. I love deep-diving the trivial things, it seems.
Blue light scatters, and red light is absorbed. Actually, some blue light is absorbed, and some red light scatters, but it’s more often the other way around. So, on a bright sunny day, all the light comes from one spot in the sky, right? But on a cloudy day, it seems to come from every direction. That’s because it IS coming from every direction, as a result of scattering. When you take the red and yellow out of the color spectrum, what is left? Well, green and blue are what remains – but it’s the blue we mostly see, because there’s not much in the clouds to reflect green light. Water reflects blue light pretty well. So, now you know the answer, and I’m sure you feel much more fulfilled.
Photographers hate cloudy days. With the red and yellow all being absorbed, what is left is mostly scattered blue, and only 1/3 of the pixels in the photographer’s camera can catch blue light. So, the camera sees 1/3 of what it could see on a sunny day. No wonder the cloudy day pictures are dull and uninteresting.
A Storm Of Photons 