COMP: Fix Colors duplicate inherited member warning.
Fix duplicate inherited member compiler warning concerning the vtk::PlotSurface::Colors ivar reported at: https://open.cdash.org/viewBuildError.php?type=1&buildid=4730716
Fix duplicate inherited member compiler warning concerning the vtk::PlotSurface::Colors ivar reported at: https://open.cdash.org/viewBuildError.php?type=1&buildid=4730716