Your starting hair colour is the single biggest factor in how this metallic tone will look. On light or bleached hair, the cool, stone-like reflection will be very visible, and the hair may appear noticeably ashier or smokier. On medium brown hair, the tone will be more subtle – you'll get a cool, muted brown with a metallic sheen rather than a dramatic change. On very dark or black hair, the colour may only show as a slight cool tint or a glossy finish, because the underlying pigment is too dark for the dye to lift much.
Porosity also matters. Hair that has been bleached, permed, or heavily heat-styled is more porous, so it absorbs colour faster and may appear darker or more intense. Previously coloured hair can react unpredictably, especially if it has a warm base – the metallic tone may mix with the existing pigment and create an unexpected shade.
Because of these variables, the manufacturer explicitly advises a strand test if you are unsure. Apply the colour to a small, hidden section, process it for the recommended time, and check the result in natural light. This is the only reliable way to know what you will get on your specific hair. Also, be aware that the final colour can look different under indoor lighting compared to sunlight.