Pure !
The colour of sugar does not depend on the plant from which it came. Red sugar, for example, is no more natural than white sugar. Both sugar beet and sugar cane produce white and red sugar.
The whiteness of sugar is due to the quality of the product, rather than the plant. The whiter the sugar, the more pure it is.
The darker the sugar, the more colouring substances (caramels) and traces of mineral salts and vitamins it contains – which is why it is thought to be more natural – but these elements are present in such small amounts that they would have virtually no effect on the human body.