Windows fix.

In windows matlab cannot display colormaps of more than 256 colors.
http://www.mathworks.com/matlabcentral/answers/47458

This is a workaround using opengl. I could not find any switch to check if the user has opengl. But I think the adoption rate is sufficient. Or should we simply display something for simple which will work on every system but is not equvialent to the plot in the paper?