There are many brands of pellet food that have heavy "colour" enhancing ingredient, of course it always claim contain "all natural colour enhancer".
To me, a good natural colour enhancer is to bring out the brilliance of the fish and darken the dark colour. However, to make the fish "red", we need to have other food to supplement. JBL pellet size are not small, the goldfish should be at 2 and half inch in size to able to feed properly.
i always like to use a yellow goldfish as example.
Attached photo shows the "brilliancy" of fish. It is not the colour that attract, but the bright and strong reflection of its colour. Not sure if i am able to explain this......hope you got what i mean......smile