The human eye is gifted at reading scenes in colour, like the pool of water and ice in the snow below.
Such blues and purples, it tells us! Such golds and dazzling whites! But, really, it is a story of absorption of a nuclear reaction 135,000,000 kilometres away, some as heat, and some as light. Reds and yellows get absorbed first. Whites indicate light scattering between crystals on the surface of the snow. Blues are the most pernicious. It takes a lot to absorb their energy and make them go away.
Of course, it’s not just white and blue that’s part of this story. Look at this crested wheat grass in the snow, at noon. Even then, in direct, yellow light, the snow absorbs what the grass reflects back to us, but, you know, it makes a lot of sense. If you are going to try to trap light within your cells and bounce it around on little mirrors until the blue-green algae at your cellular heart can eat it, it’s a good strategy to concentrate on absorbing blue light, which holds true to itself without losing energy for longer than yellow light does. Just reflect that yellow light back!
As for the blue/purple snow, anything growing under the snow cover is going to appreciate that blue’s penetrating power in the months when red and yellow light hardly makes it through the long vistas of a planet tilted away from the sun. Look below at the balance between water coming in and out of the air as the sun does this work both within the snow, through heating and reflection, and with the light reflected off the grass, that warms it in the day, then chills it at night.
Isn’t it grand how finely-tuned the Earth-Sun relationship is!