Call me anal (go ahead, I won't mind) but recipes that are as vague as this:
"Color 1 part green by drizzling a bit of the green color into the middle and knead until well blended" drive me crazy.
For the love of monkeys! Give an amount of how much food dye to use!!! Someone hired by the Huffington Post made the recipe and OBVIOUSLY knows how much they used OR Huffington photo-shop'd the finished product to look brighter.
I've got a lovely book "The Whimsical Bakehouse" and the author, God bless her, gives EXACT AMOUNTS of how many drops to use to get specific colors. She divides it into what is getting tinted: Buttercream icing (liquid gel colors) or white candy wafers (oil-based candy color).
Per 1/4 C of buttercream icing she adds 5 drops of red liquid gel. For 1/4 C of melted candy wafers, she uses 10 drops of oil-based candy coloring.
The book provides two buttercream recipes: one with part shortening and one all butter. Notes say that the color will be more vibrant with the shortening version.
Your recipe may present a bit of a challenge because it's all butter (lending more credence to the Photo-shop'd idea) or you might not be adding enough for a dough with 2 cups of butter. Would you consider using part Crisco to get the brighter color effect?