[blincoln]

Thank you.

I retried it first thing in the morning, in the dark, with my phone screen at minimum brightness, and no contact lenses in, and I got the expected result - vivid gold for my original setting, vivid yellow for yours.

After putting my contacts in, under medium ambient light, with my phone screen at medium or full brightness, I get the purple ring, but now that I'm looking for it, I can see an outer ring of gold or yellow as well.

The effects is much less pronounced if I put on my reading glasses (while still wearing contacts), so I think it must be an artifact of the contact lenses, probably in combination with the conditions they're supposed to correct (nearsightedness + astigmatism), as well as age-related inability to focus on tiny details with my contacts in.