I used a 300mm telephoto to ensure that I could select a relatively small and evenly coloured section of the generator. I have organized these in decreasing order of exposure value, starting at f/4, 1/90s, ISO 100 to f/4, 1/350s, ISO 100, each image 1/2 a stop apart. I have also carefully set the white balance on each image to be identical.
The primary difference I can see in the exposures is a progressive darkening of the yellow shade, getting muddier as the exposure decreases. The 1 stop overexposed image seems to have the purest coloration, the brightness of the over exposure enhances the yellow. I suspect that the camera has darkened the yellow towards grey at the "normal" exposure and so the over-exposed yellow is probably the purest representation of the colour. Unfortunately I did not have a hand held exposure meter with me to enable me to properly set the correct exposure using ambient rather than reflected light.
Looking at the image sequence and recording the values gives the following for CMYK:
+1 stop - C: 11%, M: 30%, Y: 100%, K: 0%
+1/2 stop - C: 20%, M: 40%, Y: 100%, K: 1%
0 Stops - C: 30%, M: 55%, Y: 100%, K: 15%
-1/2 stops - C: 35%, M: 60%, Y: 100%, K: 25%
-1/2 stops - C: 41%, M: 64%, Y: 100%, K: 40%
+1 - R: 230, G: 173, B: 20
-1/2 - R: 210, G: 150, B: 25
0 - R: 165, G: 110, B: 0
-1/2 - R: 140, G: 90, B: 0
-1 - R: 110, G:75, B: 10