Natural is the warmest and most undyed-feeling of the three — it's the color of raw, unbleached cloth before it's been processed or treated. Biscuit is similar but slightly more yellow-toned, warmer in a slightly golden direction. Linen (in the Matte range) is a polyester color that replicates the tone of natural linen — warm and sandy, but delivered through a different fabric entirely. If you're working with a palette that runs to stone, undyed cotton, and raw timber, Natural will feel the most at home. If you want a touch more warmth or a slightly more golden quality, Biscuit is the next step along.