Del Sol is the latest brand on the market to offer this, and they've just come to the UK. They work via sunlight, so your nails will be one colour in the house and another in the sun. There are twenty four shades in the range, so you should be able to find something you like!

Del Sol Colour Changing Nail Varnish: The review - Nail Polish - Del Sol

I've been trialling out the Pretty in Pink Del Sol nail varnish, an iridiscent white colour that turns into a light pink in the sun. The polish looks suitably luminous in the bottle, as it's not a pure white, rather a shimmery colour flecked with an oyster like shine. I needed two coats to get it looking suitable on my nails, but I was impressed at how fast the colour dried. As a whitish/pinkish varnish the colour was sheer and quite flattering, though I would have preferred it to be a thicker finish. When I went into the sun the colour change wasn't immediate, but over the course of twenty minutes the oyster like nails had turned into a light pink coat, with an amazing shine (not captured that well on camera).