black temporary dye

Only permanent dyes can lighten hair, but even then it's difficult and unpredictable to try to lighten more than a couple of shades. Dark hair usually turns a horrid goldy-orange if you try to lighten it too much yourself.
Black temporary dye should take on dark hair, and depending on how dark your hair is, some reds or browns will take. Blondes, pinks, greens, blues, etc. you'd have to bleach your hair first before they're likely to even show up, and they'll last a lot longer on bleached hair, too.

I don't know of any shops in the UK, but I have dark brown hair... Darkhairs like us don't go lighter without some extra effort. I do think black would work better though.

Anais