The easiest way to find out is to go to the pet shop and she what type of fish they sell. I'd say the most obvious is the way they look, swim & behave.
goldfish are not always one color because they have different species. Also, goldfish can change colors over time. They won't always be gold or maybe they won't always be white or whatever color your...
If they are the same kind of fish and it's always the same fish that's doing the chasing, then your fish are different genders. The male fish is the aggressor. It's usually not a problem, but if the...
There ancestors are gold... different colored traits over time dominated the classic gold color, while in some breeds, the gold color will dominate during the trait selecting process