The colour of snow - well, that depends.

Photograph I took of the Bow River in Calgary.

What colour is snow?  We know from experience that it is white.  And yet, the above photo would seem to indicate that it may sometimes be blue.  On the same day.  In the same photo.  In fact, snow can be both blue or white and be right beside each other.  And if all that wasn't enough, the shade of blue can also differ depending on the situation.

So, what sort of devilry is going on here?  You may already know the answer to that, and it isn't some tweak of Photoshop that has created it.  This is Nature herself and the wonderful world of white balance.

Snow reflects all the wavelengths of visible light.  The light falling upon the snow is called incident light, and it is the spectral makeup of that light causing the would-be colour change.  On a cloudy, gray day, you may find that the snow is pretty much the same colour.  Yet, on this day in April of 2017, there was an open blue sky.

Direct light from the sun would have a neutral colour balance of around 5500° K.  If the incident light hitting the snow is directly from the sun, it would appear white to someone in the same environment.  The strange thing is that if you were to move into one of the shaded blue areas, the snow there would seem white too.  However, the colour temperature of the incident light there is much higher, possibly in the 8000° to 9000° K range.  That's because of where the light is coming from.

Shadows don't have direct light from the sun, so where does the light come from?  It comes indirectly from the sun in that it is reflected light coming from the open blue sky.  There is no coincidence between the sky being blue and the snow being blue.  It is related because the blue sky is what illuminates the snow in areas of shade.

Our eyes will adjust to allow us to see blue shades of snow to appear cooler than they actually are, but the camera can't adjust for colour balance for both sun and shade at the same time.  To test this for yourself, shoot outdoors on a snowy but sunny day and play with your white balance setting.  If you know how to use custom white balance, you will find that what you see is very different from what your camera sees.  

I balanced the shades from the above photo to produce neutral coloured snow in the shaded areas.  The photo is below.  It just doesn't look right, does it?

Same photo as above, only I colour balanced it so the shaded blue areas were neutral.  Yuck.

Thanks for reading.

 Eric Svendsen     www.ericspix.com