(no subject)
I've been using the accessibility layout more and more lately, even on inoffensively formatted pages, because it makes my head hurt less and I'm becoming a little concerned. The only thing I can think is that the backlighting is bothering me (the green "accessible" screen seems much less bright than the white "normal" screen), but it never has before. Like, I spent years reading fic on this screen for at least six hours a day without headaches like this. Maybe it's reading on the non-backlit Kindle and then switching to the backlit computer screen?
V. irritating.
V. irritating.

no subject
I've never used the accessibility layout, but from your brief description, it sounds like it's a darker background? Personally, I've always found that reading light characters on a dark background is much easier on me than the 'normal' dark characters on light. (Not white on black - usually I go with something like purple or green or blue - a medium tone - on black. Bright characters Do Not Work for me. :/ ) I can't even use a light-coloured desktop picture on my computer because it makes me squint.
The Kindle won my love forever by having a sort of grayish tone overall, instead of a bright white background for those very reasons. The backlighting, for me, is definitely a piece of it, but overall the key seems to be the general 'brightness' of the tones involved.
Sorry I'm blabbering on at length about this - I've always found myself to be in a very small minority as far as reading preferences/needs go, so it's always interesting to me to see what other people have to say about it.