title: Grayscale sympy plot
body: <p>I tried to plot two surfaces in one figure, both with sympy, and change the cmap, but it doesn work, it still using de viridis colormap</p>
  <pre><code>import sympy as sp
  from sympy.plotting import plot3d
  from matplotlib import pyplot as plt
  
  x = &quot;global&quot;
  x = sp.symbols('x0:2')
  
  Fx = (3*((1 - x[0])**2))*(sp.exp((-1*(x[0]**2)) - ((x[1]) + 1)**2)) - (10*(((sp.Rational(1, 5))*x[0]) - ((x[0])**3) - ((x[1])**5)))*(sp.exp(-1*((x[0])**2) - ((x[1])**2))) - (sp.Rational(1, 3))*(sp.exp(-1*((x[0] + 1)**2) - ((x[1])**2)))
  p1 = plot3d(Fx, (x[0], -3, 3), (x[1], -3, 3), show=False, surface_color = lambda a, b, c : -c, cmap = 'gray')
  p2 = plot3d(Fx, (x[0], -3, 3), (x[1], -3, 3), show=False, surface_color = lambda a, b, c : -c, cmap = 'gray')
  
  
  plotgrid = sp.plotting.PlotGrid(1, 2, p1, p2, show=False)
  plotgrid.show()
  
  </code></pre>