the Hershey's chocolate frosting gets darker over time. It's light when you first make it, then gets darker. You could also use dark cocoa powder.
Oh and I never melt my butter...I just make sure it's very soft.
My table cakes/dessert cakes are 8 inch round, 4 layers of cake, 3 of filling. I say they serve 14-16. I use this Ateco cake marker. http://www.webstaurantstore.com/ateco-1328-double-sided-10-1-2-cake-marker-14-16-slices-august-thomsen/1441328.html
Not enough frosting on your cake. You literally have to start out with A TON of butter-cream and with the bench scraper use very light pressure.
It looks like a combination of not enough butter cream on the cake and too much pressure with the bench scrapper.