Photos would be awesome!!
(If you feel like fighting the impossible... xD)
But I'll try to give you a little list here...
Calico - Blue skin with red (or yellow/orange) and black spots, usually naucreous scales (matte and a few metallic here and there.) What's important when identifying a calico, is the BLUE skin.
Tri-colored - White skin with red, yellow or silvery spots + black. Scales can vary between metallic, matte and naucreous.
Sakura - Strong red and orange, reds are usually left on the back and head of the fish (+ tips of fins and occasionally, red lips)
Red - What most people call "gold"
Or "standard goldfish"
Silver - White goldfish (May have red eyes)
Yellow/Lemon - Really, really yellow fish.
Tancho (Japanese for "Red Crane") - A silver goldfish with a red spot on the top of the head, red-caps included.
Chocolate - This is a pretty hard color to describe, the fish looks pretty brown, and it can be warmer, colder or darker, lighter brown.
Blue and Purple - The fish will look pretty gray, but with slight blue or purple pigments.
Lavender - A lighter variety of the blue/purple color.
Any combination of two colors will simply be: Red-Black, Chocolate-Blue etc.
Here are a few photos of the more rare colors
(Here you see the blue hint in the skin)
(Here you can see the yellow goldfish among a few red ones, you see the difference
(They can look pretty gray, as mentioned, but especially when they have chocolate colored spots, they'll look blue
Hope it helped! Ask if it was unclear or if you're just wondering about something more