Teenage girls change hair colour all the time. Half the time I can't keep up with who's changed what to what.
'Who's that?' I say to my daughter as she waves goodbye to a girl with bright red hair.
'It's dyed,' she says.
'Died?' I say, fear clutching my heart. What's died? Friendship? Hope?
'Her hair?' she says, looking at me - as she often does - as if I'm slightly mad.
Every so often the boys join in. Sometimes it's quite creative - all henna and highlights. Sometimes it doesn't quite work. That's why you see so many teenagers with black hair. Black covers everything.
'He wanted to mix orange and red,' says my daughter. 'But you know when you mix orange juice and cranberry juice and it's a sort of nothing colour? That's what he ended up with.'
Teachers get really anxious about hair dye because it's seen as some kind of rebellion. (Worse than bright blue nail varnish, because there's no quick fix.) My friend's 16-year-old, whose hair is naturally white-blonde, had no end of stick from her teachers because they thought she spent every weekend covered in peroxide.
'It's true that some people,' says my daughter, 'get sort of obsessed - a different colour every week.'
If your teenager's unlucky - if the henna rinse looks orange in sunlight - the school might demand a re-spray. This means your bathroom at home awash with the kind of colours that stain the grouting. Every so often even that goes wrong, leaving an end result that's a kind of purple.
Oh, my lovely white tiles! Oh, that beautiful shiny hair covered in chemicals! Is it really creative expression or just a waste of time?
I blame Davina McCall.
Catch up on Surviving Teenagers here.