The food coloring used for farmed raised fish is natural.
This stuff is usually called NutuRose.
Alot of people are very ignorant when it comes to feed and they'll jump when an ingredient is hard to pronounce or sounds funny.
Just because something is added to the feed does not always mean it will hurt you.

Just think about the vitamins you are taking daily. It does not grow out from a tree.
In deed it is all man made in a lab.
Same thing.
Of course there are a few things which are dangerous too.
Just look for the FDA approved and do a little research before you follow the "Red Herring".