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Yellow highlighter usually disappears on a fax, because a black-and-white scan reads yellow as nearly white. Pink and orange highlighters darken enough to show up as gray shading on the other end. So the rule is simple: use pink when a mark must survive faxing, and never rely on yellow for anything the recipient has to see.
| Highlighter color | What the recipient sees |
|---|---|
| Yellow | Vanishes; the scan cannot tell it from white paper |
| Pink | Shows as light-to-medium gray shading; the most fax-safe choice |
| Orange | Shows as gray shading, usually darker than pink |
| Green | Shows as gray, but can look muddy over printed text |
| Blue | Darkens heavily; can obscure the text underneath |
A fax scanner does not see color. It measures how much light each spot on the page reflects and draws a line: brighter than the threshold prints white, darker prints black. Yellow ink reflects almost as much light as plain white paper, so it lands on the white side of that line and the mark simply never makes it into the transmission. Pink and orange reflect less light, cross the threshold, and survive as gray. This is not a fax quirk, by the way: the same thing happens with black-and-white photocopies.
A little. Bumping the scan density or contrast setting darker can drag a faint yellow mark across the threshold, but it also darkens the whole page and can turn clean text blotchy, so it is a poor trade. A better fix is to mark after copying: make a clean black-and-white copy of the page, highlight the copy in pink, and fax that. And if the highlighting is the entire point of the fax (marking the key clause in a contract, say), consider underlining in pen instead: a dark line survives any scan.
Ask whether the original was highlighted in yellow. Nine times out of ten, that is the whole mystery: the sender's page looked perfectly marked up, and the recipient's copy shows nothing, because the yellow never crossed the wire. The fix is to re-mark in pink or pen and resend. When you send through an online service, the same rule applies on the scan side: whatever device digitizes the page still sees the world in black and white.
LetterAgent sends faxes from the documents you describe to your AI assistant. You approve the exact quoted price before anything is sent, and faxes go to US and Canadian fax numbers. Fax is currently available in testing, so send times are not guaranteed, and there is no inbound fax.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
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