Back in January I piped one version of a violet (the one from Wilton's Course 2: Flowers and Cake Design). I recently learned another while reading The Art of Royal Icing by Eddie Spence. I'm not sure if it's better, but it is slightly different (and possibly more botanically accurate). You'll need a flower nail, a parchment paper square for each violet, a non-toxic glue stick, a Styrofoam brick, a dusting pouch filled with a 50/50 mix of powdered sugar and cornstarch, yellow royal icing in a bag fitted with a #1 or #2 round tip, and purple royal icing in a bag fitted with an Ateco #59 tip (or any curved petal tip designed for piping violets; bear in mind there are tips available that curve in the opposite direction if you happen to be left-handed).
These look especially charming on top of tiny desserts like petits fours and bite-sized cupcakes. Perfect for tea parties!