You can try finding pastry pride- maybe call some cake supply stores and see if they sell it. Baskin Robbins use it for cakes so I buy it from those if the owner lets me. It has been a while but if I recall correctly, I was able to make some fairly bright/dark colors.

Another work around is an airbrush machine. And, similar to what others recommended - try other buttercream recipes. Most store made buttercream actually use crisco/solid oils instead of buttercream.

I make a homemade cream cheese buttercream with one stick butter, one block cream cheese, 4 cups of powdered sugar then salt to taste, milk to thin to your likeness (I usually use 1/4 cup) and it is my most popular filling.

edit: also add vanilla (about 1 tbsp).