Hi everybody! I was asked to make a cake similar to this but I can't figure out how they did the blue. Palette knife maybe? Please help!!

Finish the cake with white butter cream, then add splotches of blue and spread them with one swoop of your spatula or pallet knife.

This was my first attempt and, which it could be greatly improved, it was very easy.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

Thanks so much SandraSmiley! I never thought of that! I'm going to try with my pallet knife.

It appears the design you posted used very small blobs of blue frosting.  I used a line of pink all the way around the top, resulting in a much larger smear of color.  It's really fun, just practice a few times.