colour of the sunlight varies, not only by the time of day, but also by the time of year – and so do the shadows

Took a second look at your sundial illustration. Not sure how you generated the image, but if it was SH3D/Sunflow (with a non-daylight-saving time setting close to the middle of a time zone), it looks like it might actually be equation of time(?). In which case I was wrong in my last post and our Azure home banter. Interesting. ok