Calfskin is a very specific type of leather. Made from the skin of a calf, or a young cow, all of the hair is sheared off and then the leather is tanned and treated. But, as with any sort of leather, it always helps to know what to look for when you're examining a finished product that claims to be genuine calfskin leather. That way you know whether or not it's worth the price tag.
Look at the calfskin. The pores in the leather should be very fine, and you'll need to look closely to be able to recognize them, if you can do so at all.
Feel the calfskin. Calfskin is very soft, supple and pliant, and it will be smooth under your touch. There will be a give when you press into it, and it will have a slight elasticity.
Examine what the item is. Most commonly patent leather shoes and leather gloves are made from calfskin because it takes a very high polish and it's very flexible. Items like vests, jackets and pants aren't as often made from calfskin because of the cost. If calfskin is used then these items they will be much more expensive and the price should reflect this. If the item is very reasonably priced, it probably is not calfskin.
Calfskin can be dyed almost any color though, so that is not a factor in determining if a piece is real or not.