What do you mean by professional icing. Professionals use a whole bunch of different kinds of icings. I frequently cover chocolate cake with white buttercream so color doesn't really matter.
Professional style buttercream aren't all that sweet. More buttery.
Something to keep in mind, if you do make a buttercream or fat based icing. You can't use the food coloring that you buy in the grocery store. I tried that recently for my son's cake. I made an italian buttercream like we do here in the bakery, but I wasn't thinking (since in the bakery we don't use any food coloring) and I added those colorings. They are water based and did not mix well with the butter. I used almost a whole bottle and still got very pale colors and you could see drops of it in the frosting.
But to answer your question. I think that both pink and lavendar go will with chocolate.