I have naturally mousey hair, with a good smattering of greys 
I usually dye it every few months. I was using John Frieda medium chocolate brown, but it always comes out too dark for the first few weeks, until it has washed out a bit. Last time I tried medium ash brown, but after a few weeks the greys were showing through again.
I want a medium chestnut brown colour that looks natural and covers greys! Any suggestions?