I have been pondering the same question
My guess is those were piped on in RI and then handpainted with lustre dust or Luck's brand Pearl Shimmer.
I have the shimmer in both gold and silver and it works very well. This can also be accomplished using lustre dust mixed with a clear alcohol; lemon extract, rum, gin or vodka. HTH.
I agree with cakediva-pearl dust or luster dust painted on the buttercream or royal scrolls. BTW, really pretty cake-that should be fun to make. Post pics!!