Reminds me of my one devious professional hack.

Back in the 1990s I supported a website whose users were all in our local business group. It was mostly html tables, with black text on a jarringly bright yellow background.

Asked my users if I could change it to something more subdued. All said “good idea” except for one adamantly stubborn person who threatened much commotion if anything changed.

So, every week or two I slightly tweaked the background color such that each week’s change wasn’t really noticeable.

After 6 months the brightness was exactly where I wanted it to be, and the stubborn user was none the wiser.