How will shade 4.0 Dark Chestnut look on my current hair colour and grey coverage?

Shade 4.0 is a dark brown with a warm chestnut undertone. On natural hair that is already dark brown to black, the change will be subtle — mainly a refresh with added warmth and shine. On medium to light brown hair, expect a noticeable deepening and a richer, more even tone. If you have a significant amount of grey (over 30–40%), the chestnut nuance will appear brighter on those strands, creating a natural-looking highlight effect rather than a flat, uniform block of colour. Previously coloured hair, especially if it has been lightened or toned, may absorb the pigment more intensely, so the result can come out slightly darker than on virgin roots. Because this is an oxidative permanent dye, the colour develops inside the hair shaft and will not wash out; regrowth will be visible after 4–6 weeks. For the most predictable outcome, do a strand test on a hidden section using the exact mixing ratio and development time you plan to follow.