Add color as a parameter to phonon_bandplot #265
Description
A proposed change/contribution to add the parameter "color" to the function "phonon_bandplot". This is defined with a default of "None" in every subroutine/method all the way down the the plotting code, except at the top level. Adding it to the top level would allow multiple band structures to be plotted in different colours on the same axes, through the python interface.