I created a copy of a the Shaded Mode and changed Surface Edge Settings>Thickness to 0.
Initially, the output looked like this (#1)
then it changed to look like this (#2):
I searched through the settings comparing the default Shaded to my Shaded Copy and the only thing I could find different was the Thickness setting.
So created a new copy of Shaded Copy and changed the thickness and it looked like #1—for a while. I did a Make2d and change some views then I noticed that it looked like #2.
So Created a third copy of Shaded and just changed the thickness setting and it looks like #1 (for now). I have gone through all the settings and cannot find any difference among my three copies of Shaded.
I am trying to figure out why I am getting a difference in brightness in the display modes (and why they appear to be spontaneously changing)./
I don’t know if this helps,. but I saw that I can export INI files for the display modes. I did that for the copies that produce two different displays (attached). I ran diff on them but it shows a plethora of differences between the two when I cannot find any difference on the screen.
UPDATE: I have created new display modes based upon SHADED and over time they have all switched to the duller red color with no change in settings on my part.