Can I buy a temporary hair colour?

[Madmog]

Never dyed my hair before and just wondering if I can buy anything that just washes in and out to add a small amount of colour, for a special occasion!

Superdrug do a colour like this that is wash in wash out. It is rather subtle, although the longer you leave it in for the richer the colour will be.
It's called Colour effects.
www.superdrug.com/Superdrug/Superdrug-Colour-Effects-True-Chestnut-5%3A4/p/400947#.VXbpt1I13wo

Nice & Easy also do one that lasts for up to 8 washes.
www.superdrug.com/Save-%C2%A31-on-selected-Nice-N-Easy/Nice%27n-Easy-Non-Permanent-Hair-Dye-Light-Brown-755/p/404699#.VXbp81I13wo

When I was pregnant I used this, it's easily adjustable - leave on 2 min to gradually build or maintain OR leave 10 min for a proper change. I used the red but there are several shades.
m.boots.com/h5/cat_hub?path=%2Fen%2FScott-Cornwall-Colour-Restore-Deep-Red-Hair-Toner-100ml_1262300%2F&unCountry=uk