By refreshing your hair colour tonight.
Oh stop it.
As if you're doing anything other than watching CSI and planting tulip bulbs.
I like to use a wash in, wash out colour refresher. They take a few minutes in the shower and make your hair look gloriously shiny and lovely and totally like you've just been to Cheryl's Hair Trendz and had your $65 semi done. They're great in faded-hair "emergencies" like if you have a wedding to go to, or a saucy date or a board room presentation to a hair care colouring company, who will obviously be checking out your hair. (Probably that last one will be less common.)
I like Goldwell Love Brown (they of course do a red and blonde one too) - which encompasses a shampoo, conditioner/treatment and leave-in fluid thing that also deposits colour but moisturises your hair too. It doesn't stain your hands. It's not tricky or gloves-required-y, or tiles-stain-y, or thinking required-y at all.
Another one I have just discovered is Revlon's one, (yes, they do hair colour, and false nails too. Seriously) which is in a small round bottle and I will need to go home to get the product and tell you the name, because I can't remember it.
As we all know, brunette is The Colour Choice of winter, (shoosh, no arguments, you know it's true) as these three Foxy Friends of Fruity generously illuminate (pun intended) in this rubbish photo I took last Thursday at Sunsilk's launch of their new fashion haircare (Explanation: Akira Isagowa, Bettina Liano and Wayne Cooper have each created flash bottles with a lushly-scented, shine-inducing 'poo and condi.)