I am doing a side stencil on fondant and I was planning on using royal icing. Should I use petal dust or color spray instead?
I do the side stencils with royal. Using petal dust or color spray would just give you an entirely different effect, IMO. There is a bit of a relief with the royal, even when you use it very thin. I don't know how the intensity of color would be with the stencil, but it would still look nice, just different.
Just be careful if you put the cake in the fridge. The condensation (when you remove it from the fridge) can ruin the stenciling. I've had it happen to me.