I also have been experiencing scintillating scotoma for the past few years. I don't get the cool colors, just Widmannstatten patterns, pretty coarse grained, like a clear kaleidescope partially over my field of vision. No pain, dizziness or anything else but the visual effect. Not triggered by altitude or exertion, or anything else in particular that I can identify. Haven't seen a particularly good cgi of what I get, but one of the ones on the Wiki page is an approximation.
In fact it started the year I did my JMT through, but I do not remember ever getting it on the trail. I did discover my tinnitus on the trail, but that's another story.