Basma can be considered if you want to refresh your shade, add richer depth after henna or try a more botanical approach to hair colour. However, hair history matters a lot. Grey hair, lightened hair and chemically treated hair often have different porosity from untreated hair, so plant pigments may attach more strongly in some areas and less evenly in others.
On grey hair, basma is often used with henna in traditional herbal colouring routines because henna contributes warmth and basma contributes cool depth. Using basma alone may create a cooler dark effect, but the result can depend on how much grey you have and how resistant those strands are. If your hair has been bleached or highlighted, be especially cautious: very light or porous areas can take up plant colour in a way that looks stronger or cooler than expected.
A strand test is the most useful step before full application. Choose a small hidden section that represents the hair you want to colour, apply the prepared paste, rinse and dry it, then assess the shade in natural light. If you have recently used chemical colour or plan to use one afterwards, it is wise to ask a professional hairdresser for advice, as mixing different colouring methods can affect the final appearance.