On Friday, I sent an email with some important details highlighted in yellow. Black text on white background, key phrases in bright yellow highlighter. A holdover from the paper era of the ’70s and ’80s, when yellow Hi-Liters became ubiquitous in every office and classroom.
That evening, I was reviewing replies on my iPhone. My phone shifts to dark mode at night—white text on a dark background. I scrolled past my original message and stopped. The highlighted text was now white on yellow. Nearly unreadable without squinting.
It occurred to me immediately: the age-old practice of yellow highlighter no longer works when you can’t predict whether the viewer will see your content in light mode or dark mode.
The Assumption That Broke
Yellow highlighting works because of two things happening at once. The yellow block catches your eye against the white page—it’s the only color in a sea of black and white. And the black text remains perfectly readable against that yellow background because the contrast is still high enough.
But that second part assumes the text stays dark. In dark mode, the text flips to white or light gray. White text on yellow has almost no contrast. The highlighting still catches your eye, but now you can’t read what’s inside it. It doesn’t just fail to emphasize—it actively obscures.
This isn’t a bug. It’s a collision between a formatting convention from the paper era and a display paradigm that didn’t exist until recently.
What Works Instead
If you’re formatting content that might be viewed in either mode, you have a few options:
Bold text works regardless of color scheme. It’s purely about weight, not color.
Colored text can work, but choose carefully. Red or blue tends to remain readable in both modes, though some email clients strip color formatting entirely.
Bullet points or numbered lists for key items draw attention structurally rather than chromatically.
Or just accept that some readers will see your formatting differently than you intended. That’s the world now.
The Broader Point
We carry a lot of assumptions about how people will see our content. White background. Standard fonts. Left-to-right reading. Desktop-sized screens. These assumptions erode gradually, then suddenly.
Dark mode adoption has accelerated. Estimates vary, but somewhere between 70-80% of smartphone users have enabled dark mode on at least some apps. It’s the default on many devices after sunset. Every piece of formatted content you send—emails, documents, presentations—might be viewed in conditions you didn’t anticipate.
Yellow highlighter isn’t the only casualty. Light gray text that looks subtle on white becomes invisible on dark backgrounds. Certain chart colors lose their distinctiveness. Screenshots of light-mode interfaces look jarring when embedded in a dark-mode context.
The fix isn’t complicated: before you send something with formatting that depends on background color, consider what happens if that background inverts. If the answer is “it becomes unreadable,” pick a different approach.
The humble yellow highlighter served us well in the paper era. It’s not obsolete—it still works fine on paper. But on screens, in 2026, you can’t assume everyone’s looking at the same canvas you are.