The base colour is one of my favourites... Nail Polish by H&M in Blue My Mind. Two coats of that, followed (once dry) with a deep curved tip of black going to almost halfway down the nail. I used a black polish from an FCUK gift set. To help, you can draw a black curved guide line with a nail art pen before filling in the tips.
Once the tips are fully dry, use a white nail art pen to add 5 white stripes to each tip. Using my trusty Models Own Nail Art Pen I started with the centre stripe to make sure I created an even fan shape.
To finish off, before adding top coat, I actually went around the bottom of the curve with a black nail art pen just to neaten up the lines but that's not necessary. I'm ridiculously anal when it comes to things like that! Even now, looking at the pic it's annoying me that the outer edge of the curve on my little finger isn't filled in properly... best go off and rectify that!