The way I've seen this done in the past is to paint your outline colour first, then tape of your tips and paint your second colour, leaving a little bit of a margin around it. I sort of did it like this, but minus the tape - I just freehanded tips on in my outline colour. Not as neat as you'd get with tape, but I really hate the stuff lol.
Naturally what little sunlight we had disappeared when I went to take pictures of these! I used Jessica Ruffled Bottoms and Layla Gold Idol.
My nails are really curved, so you can't really see that there's an outline at the sides as well! So here's a side shot just to prove they are there lol.
Thanks to the rubbish British weather, Gold Idol looks like a rather poor scattered holo here. It's actually an AMAZING really strong linear holo. Here's a picture with flash that shows it much better!