ADo you mean airbrush?
AI don't think that is hard to do, just practice on some paper first. Don't hold the brush too close and spray in layers to avoid drips x
For sure this gradient is easiest to achieve with airbrush.
HOWEVER: I see 2 different colors of blue used. A "sky" blue gradient that travels 100% up the tier then a 2nd, shorter gradient of darker blue.
O.k. great, I'll give it a try tonight :) wish me luck :)