While the level of residual sugar plays a role in the finished style of a wine, the color of all wines—and the color of everything we see, for that matter—is determined by residual light. Any systematic analysis of wine begins with a careful observation of color and what we see is the result of light waves being reflected by compounds in the liquid.
The plant pigments associated with flower and fruit coloration are known as flavonoids, with the most commonly known being the anthocyanins—derived from the Greek words for flower and blue, anthos and kyanos. These water-soluble pigments found in leaves, stems, roots, flowers, and fruits show us red, purple, or blue hues depending on their pH levels.