Sugar is naturally white. When sugar is extracted from sugarcane or sugar beets, it is typically a mixture of sugar molecules, plant fibres, molasses, and other non-sugar materials. These impurities can give the sugar a golden or brown colour.

To produce white sugar, the raw sugar undergoes a refining process that involves multiple steps:

1. The sugar is first dissolved in water, and then it is treated with lime to neutralise any acids present.
2. The solution is then heated and filtered to remove the plant fibres and other solid impurities.
3. Next, the solution is treated with activated carbon to remove the remaining colour and impurities.
4. The solution is then boiled to evaporate the water and produce crystals of pure white sugar.
5. The resulting sugar crystals are then washed and dried to remove any residual molasses or other impurities, resulting in the final product of white, granulated sugar.

Source: sugar.org