When using scalar coloring, if vtkScalarsToColorsPainter decided to use
a texture for mapping the scalars to colors, we ended up with the
surface color bleeding through the texture. This commit ensures that
such bleeding is avoided.

We don't simply use glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,
GL_REPLACE), since that results in the diffuse highlights being lost.
By enabling GL_COLOR_MATERIAL and calling glColor3f(1,1,1), we follow
the same lighting/coloring path as we would when not using the texture
for scalar coloring.

Change-Id: I9c4db15dd0db699d5d045fa7ae27696d18828988