Can anyone explain me why the blue sky reflects in the shadows?

[Nanuk]

Hi again!

When reading some books about oil painting I already understand that cast shadows are not dull; rather rich and filled with colors. One concept that still puzzles me is that some painters introduce blue tones, over the shadow areas, and say that they correspond to the sky reflection.

I have some difficult to understand how is it that, a shadowed area contains blue tones, reflected by the sky...

Can anyone explain this to me, please? This is quite confusing...

Thanks in advance

Best regards

Nanuk

[Patrick1]

You can think of a blue sky as a large, diffuse blue light source. The sun will be the main light source, but the blue sky will be a subtle, secondary light source that influences shadow colors.

Take a look at the color of cast shadows on asphalt on a sunny day with blue sky. It's not black or dark grey but slightly blueish or purplish. If there's a black object nearby, look at it for comparision. In snow, or other white objects, it can be much more than subtle; snow shadows are often surprisingly bright blue or purple.

Just observe nature...I guarantee that very soon you'll be seeing lots of colors that you never knew were there...not just in shadows but everywhere.