So, I'm turning 44 in a few weeks, and I'm working my way up to a proper mid life crisis. I don't have the dough to blow on a sports car, so the blue hair will have to do the trick.
The recipe I followed is two applications of 30 vol bleach, then paintbox "blue velvet". I'm not expecting it to stay vibrant for terribly long. Once it's faded I might try a purple, as that's traditional for women in engineering.
Edit: and after a fortnight, I went totally to town. Thanks Mary!