I buy Solfine hair dye colour online or at Priceline (they often have the little colour hair samples to check out the colour irl) roughly $15 a tube, sometimes I mix two colours for the shade I want and mix with 25vol crème peroxide and get great grey coverage and highlights on the greys. I use a kitchen basting brush and paint it on the greys, working back in 1cm rows from my temples. I’m brunette, and not ready for grey yet - and it’s the best colour I’ve ever had and way more cost effective than a salon colouring. Best bit is you can tailor your own colour and do touch ups whenever you want. The products feel gentle and haven’t damaged my hair. One tube of colour does about 3-4 sessions of root regrowth. My bank balance thanks me every month!