i always here about goldfish being brown to black when small and changing to gold. i, for one, have had a gold one grow black patches. that was weird. then again, my predatory fish also left it alone for a few months...

i have read on cichlids being kept outdoors temporarily. the come in with bright beautiful coloration that fades once in the aquarium. perhaps it is the same for goldfish?

i know that doesn't help much, but maybe it gives you a start.

Change in environment (pond to indoors) can also change coloration.

In my pond experience, true shubunkin breeding will result in babies that are hatched with the calico patterning to begin with - which doesn't really change all that much from hatching to adulthood. With the "mutts" as I call them (cross between comets/shubunkin/koi) the babies are born dark. Comet/koi breeding usually results in dark babies that may or may not change colour in the subsequent years. Usually the orange color of the comet, with a white belly. The shape is more koi shape than comet shape. True comet breeding the orange colour appears earlier than the comet/koi cross breeding. Comet/shubunkin cross-breeding in my pond have resulted in dark babies that eventually turn comet orange and have longer flowing tails than comets have.