expr = 5 * (cos(x) - 0.2 * sin(y))**2 + 5 * (-0.2 * cos(x) + sin(y))**2
p1 = plot_contour(expr, (x, 0, 2 * pi), (y, 0, 2 * pi), "z",
     {"cmap": "coolwarm"}, show=False, grid=False)
p2 = plot_contour(expr, (x, 0, 2 * pi), (y, 0, 2 * pi),
     {"colors": "k", "cmap": None, "linewidths": 0.75},
     show=False, is_filled=False)
(p1 + p2).show()