That looks like airbrush to me. Fun cake
I would use grey non-toxic chalk or petal dust to add the shadow.
I would use petal dust to achieve that look.
Thanks! I will have to order some grey...
I think it's airbrush myself -but you should call their cake shop and ask them. I called Courtney's Cake Nouveau shop to check on a color of blue they used, and they just yelled back to the shop to get the answer from her. That could save you a lot of trial and error if they have already figured it out.