You may. This shampoo for blonde hair, however, was specifically designed to improve the appearance, shine, and texture of highly damaged or over-processed blonde hair. If someone who is brunette or red used this product, they would see colour-preserving, smoothing, shine, and fibre-alignment benefits but it has not been optimised to improve brunette/red colour.
We recommend that brunettes use Brilliant Brunette Multi-Tone Revealing Moisturising products, which have been optimised for the needs of brunette colour-treated hair. We recommend that colour-treated reds use Radiant Red Colour Protecting Shampoo and Conditioner, which have been optimised to meet the needs of red colour-treated hair.