Unfortunately browser's don't really give you an easy way to control this. Changing system-wide settings just because one website is bad is quite the ask ask.

Same, and a bit of a persistent queasy feeling. I think it’s something to do with how it’s slightly off white but pulsing, so your brain tries to cancel it out.

It reminds me of the feeling after surfing when you lie in bed with your eyes closed and still feel the waves going up and down.

As a second data point, I added the same effect to my blog back in, I don’t know, 2002 and all my friends complained about getting a headache as well, so I turned it off

For some reason it never had that same negative effect on me

I suspect that it basically confuses your brain because it tries to adjust the "white balance" so that the background becomes normal white. But the background is just saturated enough and changing so quickly that it just can't follow.

Nice, thank you!