John. I think there is the possibility that your camera may
not be lying.
Gazza's Q about the pol filter is interesting. If the
light being reflected from the
MC is in fact plane polarised (though the curved surfaces would affect its incidence
at the camera) then it might help. But I think you're seeing that camera's response
to progressively brightening
red light. Note that next to the
yellow it is
white.
I don't know of any particular setting that would eliminate it (other than another camera).
Perhaps (this is basic) check that the color space the camera is set to is the same as
the program you are using to process the images (usually sRGB).
In addition, the
samples shown here do not inspire confidence in the reproduction of
the reds. Yes, the raws look better than the jpegs. Also, check your color styles.
See further down the page in that link. And a worry: the article does not even
mention that glaring fact.
Maybe try some other (incl non-iridescent) red subjects for a better perspective of
this phenomenon.