Today I conducted an experiment that worked (bear with me here)
I bought a bog cheap brown mascara and used it to "paint over" the (not that many) grey hairs in my parting. And blimey - it worked. grey hairs gone, no weird texture to hair, colour match pretty good. Slightly worried as to what will happen if it rains (couldn't get waterproof mascara) but chuffed with self so far.
Is this a trick everyone else knew about and never crossed my radar before?