Light is composed of waves. The color of a light wave depends on its wavelength, with longer wavelengths appearing red and shorter wavelengths appearing violet. However, most of the light we encounter every day is a combination of many different wavelengths and thus many different colors. The combination of these different colors produces white light. This observation was made as far back as the 1600s when Sir Isaac Newton realized that passing white light through a prism caused it to split up into its various color components – the result is a rainbow that displays the entire visible spectrum from red to violet.
Certain objects appear white based on the principles of the wave characteristics of light. For example, an object appears blue because that object absorbs light of all other colors besides blue and reflects the blue light back towards the observer’s eyes. Although it is somewhat counterintuitive, this is how we perceive the color of an object. If you have your doubts, you could try shining pure violet light on a red object. Since there is no red in the shined violet light, nothing can be reflected back, and the object will appear black – the color that results when no light is reflected.
Snowflakes are miniscule crystals of ice that contain intricate surface patterns on every face. This complex geometry acts as a mirror, reflecting nearly all the light that strikes it. This effect, compounded with the large amount of surface area exposed on the exterior of each crystal, is what causes snowflakes to appear white.