Hey

I did a little research, but I didn't find any answers which would help me... I'm asking about the colors of common and comet goldfish. They are usually yellow, orange, red or white... Or red-white combination, and shubunkins which have black patches.
Anyways, a few weeks back I bought 2 really beautiful orange babies with a black line across their back and fins... But after a few days, the color vanished and they turned into pure orange. Some time later, I got 3 larger fish, one of them being gray and 2 others with a black line and fins. The black scales aren't shiny, but other have a distinct metal shine. Is there anything I can do to prevent them from recoloring?
What happens when a fish looses it's color? And I'm hard-pressed to find any information about black color on comet/common goldfish.
Does it have anything to do with food? light? water quality? changing from pond (masive breeding) to aquarium? stress?
Thnx for answer

gray fish black patched fish
(
Link is not visible to guests. Please register to view.)
(
Link is not visible to guests. Please register to view.)