All spirits – whether they be vodka, gin, whiskey, tequila, rum, etc – come off the still as a clear liquid. This may come as a surprise to a lot of people because they are accustomed to drinking “brown” spirits such as whiskey and brandy. The spirit starts as a clear liquid because regardless of what the raw material is that is distilled, it is vaporized and re-condensed in the still. The color does not carry over in this vaporization.
So where does the spirit pick up its color? In the case of whiskey, brandy, or dark rums, the color comes from time spent in a charred oak barrel. The clear spirit, or white dog, is barrel aged for a period of time that can range from months to decades. While in the barrel, the spirit interacts with the wood picking up new flavor profiles from the tannins and vanillin in the wood.
The spirit also oxidizes and some will be lost to evaporation. This is commonly known as the angel’s share.