[Evan Snyder] gave me this interesting link - http://jonathanclark.com/diary/flare/ - on the subject on lens flares. The number of blades making up the aperture of the lens influences the shape of the lens flare produced, so that a six-bladed aperture, for example, would produce a hexagonal sun flare effect. Evan suggests the possibility that the name was inspired by a documentary, or even one of Hexagon Sun's own films, with special meaning to BoC, featuring a prominent turquoise hexagonal sun flare. An intriguing possibility, and a very interesting link. (You can also find photos fitting this description at WarpRecords - go to Artists, BoC, and look at the Gallery photos).
Not specifically in relation to this track, but in a wider sense (Hexagon Sun, the kaleidoscopic images on Geogaddi, etc), here are comments from the NME Interview:
"What's the significance of hexagons to you?"
"Marcus: "The hexagon theme represents that whole idea of being able to see reality for what it is, the raw maths or patterns that make everything. We've always been interested in science and maths. Sometimes music or art or drugs can pull back the curtain for you and reveal the Wizard of Oz, so to speak, busy pushing the levers and pressing buttons. That's what maths is, the wizard. It sounds like nonsense but I'm sure a lot of people know what I'm talking about."
Various bits of speech, repeated elsewhere in the track. It's hard to make out much, but here's [DC]'s guess at some of it:
"there's been a [release/leak]"? [female voice near start] - 0:36, 1:58
"Oh, ... I know" [Scottish girl] - 1:14, 2:35
"Just slightly" [different Scottish girl] - 4:29
"... just [come in at the] end, right?" [English man] - 4:19
"fan - tastic" [same man?] - at about 4:38.
The girl speaking at about 1:22 and 2:44 sounds (to me) like the same one who speaks all the way through all 3 live recordings of BoC at ATP, Lighthouse, and Warp - which adds to suspicions that these are recordings of people talking at the the Hexagon Sun studio, as the title of the track would suggest.
'Hexagon Sun' refers to the studio of Boards of Canada in East Scotland, but also to the collective of musicians and friends of Michael and Marcus.
This song has been speculated to contain samples from inside the Hexagon Sun studios. These samples have also been said to match up to voices in the recordings of some live shows backing up the claim that they are from the inside.
Turquoise Hexagon Sun might be a reference to the Hexagon Sun "collective" of musicians and artists who work at BoC's Hexagon Sun Studio in the east of Scotland.