This is only superficially trivial.

Ice is transparent. Snowflakes on the other hand are not solid ice but very complex crystals. Therefore there are so many reflections and refractions going on in a pile of snowflakes that incident light is scattered back in the end. So far, so good.

Now here comes the catch.

Sunlight is not white, but yellow.

Well, actually, it is white but it gets yellow because of Rayleigh scattering in the atmosphere. See also "Why is the sky blue?".

So why does the snow not look yellowish?

By the way, Webster 1913 defines white as "the color of pure snow", so we might be running in a circle here ;) In my opinion that's a bad definition because it does not mention what kind of light is shining on the snow.

But anyway. The point is that our brain makes it so! It apparently compares the light going in with the light going out. If it's the same color, the object is white. Therefore white paper looks white to us even under colored light - but when you take a photo, it is definitely colored as well.

So why is the snow not at least yellow on photos?

That as it turns out, is entirely due to the film used! It is designed so that "white" objects in sunlight look white. This as also the reason why one has to watch out when using a digital camera, because the CCD in cheaper models often has issues with the color balance rendering the snow yellowish!

wrinkly points out that the blue of the sky and the yellow of the sun might combine to white again. I cannot refute that. However, it is still true that snow can look yellowish on a bad photo, so apparently it does not quite add up!

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