I have a pond at home with a new pet koi named spot
Koi is actually an informal group of the Amur carp. It's a colored variant.
oh ok, since I am a novice in Koi fish, I always thought they were like goldfish
That's understandable, but Koi varieties are distinguished by their colors and patterns.
mine is orange and white, is that a common color?
They were originally eaten as a food dish, but they have varied colors. Those are common colors that I have seen before.
where are they originally from, China?
They were originally found in Central Europe and Asia, so I would say yes.
my pond is real small, about how big do they get
The Amur carp was found in the Jin Dynasty, so it's at least smaller than the Jin Dynasty.