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When making a vtkLookupTable, setting the desired color for NaN data points using SetNanColor works fine if called as the first thing, before using SetTableValue.

However, SetNanColor fails if done after setting up the other colors using SetTableValue. The specified color is not used to display NaN data points. Instead, the default reddish brown NaN color is used (or the color specified in a SetNanColor call placed before any SetTableValue calls). Oddly, GetNancolor still correctly returns the color supplied to SetNanColor.

This bug was seemingly introduced in VTK 7.1.0 and is still present in 7.1.1. Observed in Python 3.5 and 3.6.

Code to reproduce:

from __future__ import print_function

import vtk
import numpy


def main():
    """
    :return: The render window interactor.
    """

    chessboard_resolution = 5
    n_lut_colors = 256
    data_max_value = 1

    # Provide some geometry
    chessboard = vtk.vtkPlaneSource()
    chessboard.SetXResolution(chessboard_resolution)
    chessboard.SetYResolution(chessboard_resolution)
    num_squares = chessboard_resolution * chessboard_resolution
    #  Force an update so we can set cell data
    chessboard.Update()

    # Make some arbitrary data to show on the chessboard geometry
     data = vtk.vtkFloatArray()
    for i in range(num_squares):
        if i == 4:
            # This square should in principle light up with color given by SetNanColor below
            data.InsertNextTuple1(numpy.nan)
        else:
            thing = (i * data_max_value) / (num_squares - 1)
            data.InsertNextTuple1(thing)

    # Make a LookupTable
    lut = vtk.vtkLookupTable()
    lut.SetNumberOfColors(n_lut_colors)
    lut.Build()
    lut.SetTableRange(0, data_max_value)
    lut.SetNanColor(.1, .5, .99, 1.0) # <------ This color gets used (light blue). If comment out, default reddish brown gets used.
    for i in range(n_lut_colors):
        # Fill it with arbitrary colors, e.g. grayscale
        x = data_max_value*i/(n_lut_colors-1)
        lut.SetTableValue(i, x, x, x, 1.0)
    lut.SetNanColor(.99, .99, .1, 1.0) # <----- This color (yellow) gets ignored! ...except by GetNanColor

    print(lut.GetNanColor())  # <-- Prints the color set by the last SetNanColor call above!

    chessboard.GetOutput().GetCellData().SetScalars(data)

    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(chessboard.GetOutputPort())
    mapper.SetScalarRange(0, data_max_value)
    mapper.SetLookupTable(lut)
    mapper.Update()

    actor = vtk.vtkActor()
    actor.SetMapper(mapper)

    renderer = vtk.vtkRenderer()
    ren_win = vtk.vtkRenderWindow()
    ren_win.AddRenderer(renderer)
    renderer.SetBackground(vtk.vtkNamedColors().GetColor3d('MidnightBlue'))
    renderer.AddActor(actor)

    iren = vtk.vtkRenderWindowInteractor()
    iren.SetRenderWindow(ren_win)
    ren_win.Render()

    return iren


if __name__ == '__main__':
    iren = main()
    iren.Start()