Hi Patti, E. Black Prince really turns very dark during the warm, dry summer days, and at a point it will appear to be closing down its leaves, if it really goes way too hot. It will slowly return and open up again when cooler temps return.
This was taken last 2Sept2014, temps has been in the upper 90's and very dry, so plant went on semi-dormancy:
This was taken last 20Nov2014, E. Black Prince going back to its plump and more open appearance as, temps have cooled down nicely in Fall.