I was intrigued to see this photo, and to hear of observations by David, whom I have not seen in many years.
David’s comments reminded me of the advice to astrophotographers about capturing star colours on film (or electronically I suppose). Defocusing the camera lens reduces the intensity of the star image and allows the colour to be recorded much more clearly. I think there is an image by David Malin showing this effect, where star images were progressively defocused.
As I recall, David has an excellent location. The former perihelic opposition could have been 1971, 1973 or 1975.
The red colour of Mars to the naked eye was modified by the recent large dust storm, with several observers seeing a more yellowish tone. Now it seems more nearly normal. I would encourage this sort of observation.