Color Parrot - Variation in neutrality with angle of incidence?

It has been conjectured that, owing to the difference in the transmissive chromaticity of the Color Parrot between its central spot and the surrounding annulus, it might exhibit a chromatic response that would vary with the angle of incidence of the arriving light on the diffuser face.

We recently ran a basic test to examine this possibility. We used the same "snooted" incandescent lamp we used as a source for the basic directivity pattern measurements.

We first took a "white balance reference frame" with the camera/diffuser axis aimed directly at the test source. We then set CWB using that as a reference.

Next, we took test frames with the axis still pointed at the source, with the axis 15° to the left, and with the axis 30° to the left.

We then determined chromaticity at the center of each of the "corrected" frames.

The departure from relative neutrality was inconsequential at either angle.

Thus it seems that, at least over this modest range of angles, the transmissive chromaticity of the Color Parrot is independent of angle of incidence. It may well shift for greater angles, but I did not feel it warranted to test there. (Because of the reduced sensitivity at such angles to the light from the test source, we must be more scrupulous to avoid extraneous light at those azimuths, and I didn't want to bother covering up all the the trivial sources around the house.)