How to pipe a beautiful cake retro vibes rosette cake!

Materials
• Three 8" round cake layers (Vanilla cake recipe baked in three pans for 27 mins - http://cake.style/2016/03/01/vanilla-... )
• Sweet crusting American buttercream - http://cake.style/2016/03/01/sweet-bu...
- 1.4kg blue - Americolor Electric Blue
- 250g pink - Sugarflair Pink
- 80g green - two parts Americolor Avocado and one part Americolor Mint Green
• Piping tips – #1M - blue, #21 - pink, #352 - green
• 3 Piping bags
• Angled spatula
• Cake scraper
• 9" cake board