Grey is the natural colour of the carp the goldfish was developed from.
no it is natural like the colour in your skin
This is probably just a natural color change. This is common in goldfish. If you notice any strange behavior, take it to the vet.
Goldfish see in color.
Different types of goldfish food typically don't affect the colour of goldfish, however there are some specific goldfish foods that may enhance the color of goldfish- but do not change its overall color.
The color of cadmium is a metallic bluish-white color
the colour of chalk(calcium carbonate) in its natural state is white.
Nothing. A goldfish is a goldfish, not a gold fish.
the color of aluminumm in its adonized state is a silvery metalic color that is not much different from that of stainless steel.
It is a redish brown color.
theoretically, yes! a goldfish will loose color if you put it in the dark. Allow the fish to get NON-direct natural sunlight (don't ever place a goldfish in direct sunlight though) and it should return to its natural color within a few weeks to a few months if you feed it properly. you can get color enhancing foods at the pet store, which will help :) proper nutrition and care make for a healthy, colorful fishy friend!
Silvery white