Since our blog post on quality checking your scans mentioned the perils of scanning documents marked up with a blue highlighter, we’ve gotten a few questions from people who want to know what color highlighter they should use on their documents, if not blue. Choose the wrong color, and you may end up blacking out or obscuring important information on the scanned copy of the document.
We decided to do a little test to try to answer this question and were very surprised by our results.
For this test we used a set of new Sharpie brand highlighters in five colors: blue, green, orange, pink, and yellow. After highlighting some text with each color highlighter, we scanned the document with a Fujitsu 6110 scanner in black and white using the latest Scan123 scanning software.

The text that was highlighted in yellow, blue(!?), and green is clearly legible. You may be able to read some of the line in the middle, which was highlighted in orange. By far the worst, however, is the last line, which was the pink highlighter.
Needless to say, we were surprised by these results, especially the fact that the text highlighted in blue was so easy to read. This runs contrary to conventional wisdom that text scanned in blue and other dark colors will not show up well on a black and white scan.
Just to be sure, we ran the same test again on a Visioneer flatbed scanner and got very similar results. Yellow, blue, and green were good; orange was poor; and pink was terrible.
We also scanned the same document in grayscale and in color and found that all of the text, no matter which color it was highlighted in, was perfectly legible.
We’re not sure exactly why the results of this test differed from last time. Some online commenters have suggested that the brand of highlighter you are using can make a difference. It may also depend on your scanner model, scanning software, and scan settings.
If I had to choose a color of highlighter to recommend for use on documents that will be scanned in black and white, I’d have to go with yellow or green due to the differing results for blue. But if I can go beyond choosing a color, what I’d really recommend is doing this test for yourself. Seriously, this only took a few minutes to do. Just try it for yourself with your own equipment that you will be using.
If you are a Scan123 customer that needs to scan documents that have been highlighted in a color that is obscuring the text on your scans, put in a support ticket, and we’ll work with you to adjust your scanner settings appropriately.