I swear by my ChefMaster no fade purple.
In the cake below, the fondant was pre-colored Satin Ice purple. The border is hard to see because of the angle of the photo, but it's a very dark purple. I made it with a good bit of CM no fade purple & some AmeriColor super red & royal blue until I got the shade I needed.
I checked the flavor, and it was fine. No funny taste, even though the color was so dark.