Not that I know of.
The problem is that Excel uses the same data table to generate the graphs, and doesn't distinguish between different areas of the graphs, (eg it doesn't know that some of the data is real, and some is projected). So when you right click the body of the graph and choose Format Plot Area, or Format Data Series, (for the area underneath the plot points), there is nothing to specify which parts of the data is real or prjected.
I suppose you could use 2 graphs, with the same dimensions and place them side by side, but that would be difficult to achieve a smooth join even if you choose "no borders", "No data legend" for the Y axis on the right hand graph, and in "Chart Options" under the Axes tab, clear the "Value (Y) axis.
I am creating excel graphs that project data into the furure. what i would like to do is make the body of the graph have two colors - one for the past and another for the future. is it possible to put two different colrs in a graph - how? thanks