Using the Rimmel London Rita Ora collection
1. Paint the entire nail with a white base.
2. When dry, apply a baby blue polish in strokes starting from the bottom right-hand corner of the nail up towards the left-hand side. Leave a curved section of the white polish exposed at the tip. Add an extra coat of blue to intensify the colour.
3. Repeat the last step with three more bright colours (Adam went for pink, orange and blue) to create a rainbow effect. Always leave a curved strip of the last colour exposed. Load your brush with less colour as you work down the nail - you don't want to flood it with polish.
4. When dry, add some glamour with a thin line of silver glitter polish stopping in the centre of the nail. You can use a striping brush for this.
Source : http://www.cosmopolitan.com/uk/beauty-hair/g3477/the-best-summer-festival-nail-art-designs-how-to/