Black Copper Marans were the first variety recognized. Here's B.A. Davis' Black Copper rooster:
White and Wheaten are also recognized.
Blue Copper Marans aren't yet a recognized color variety, in Marans or any other breed. They are blue where Black Copper Marans are black. Blue Copper reproduces the same way other blue varieties do: incompletely. Typically, about a quarter of the offspring from Blue matings are black, a quarter are splash and half are blue.
Ryan Masterson sent this chart to explain it: