It will likely turn brown as it dies. My guess is that "sheet moss" is any moss that is gathered from outdoors and could represent any number of species from any number of habitats.

Thanks. I understand it was collected in a damp, shady area on her property. Do you suppose if it gets almost dry and then sprayed with a hand sprayer, it will retain some of it's color?

Perhaps if it is grown in a shady spot and sprayed with water of the correct pH.