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When communicate with people over a drawing I often like to mark it up to show where areas of interest are. The instinctive choice for color in the situation tends to be red, because red is often visually catching (i.e., markup with red pen). However, what is the best color to use if you are concerned about being visually friendly to people with color blindness? Yellow is often difficult to notice, and blue and green typically do not pop out.

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  • I'm glad you are trying to make things more accessible to others! In this case you're overthinking it. We notice markings mostly because they're distinct from the rest of the image. The red just helps people see them more quickly, but sufficient contrast can do that job also Feb 15 at 2:00

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A mark has several components.

Shape You can use a black marker to draw a circle, x or whatever on the drawing.

You will notice it if it has enough contrast. Using a pencil is less contrasting than a marker, not only by the thickness of the mark but also because of lightness contrast.

And after those visual clues, we have color contrast. Even without thinking of color blindness, we can think of a case where red is a bad choice, for example, adding marks to a picture of several firefighters and emergency trucks. Red will not be noticeable over a red truck.

So, to maximize contrast even for non-color-blind people, use all the other techniques.


Now you can think of color blindness, which has different flavors.

You can take a glimpse on that with this simulator: https://www.color-blindness.com/coblis-color-blindness-simulator/


I would say in your case, color does not matter as long as there is enough contrast of shape and lightness.

When is more necessary is when you have different marks, that are (I repeat) different, but at the same time, are not... Yes, it was a tongue twister.

If you mark one circle red and one circle green, meaning green is ok and red not, you have a problem. They are different marks, that have different meanings, but at the same time, for a color red-green blind person, they are not different. So you can implement different thicknesses, add an "X" or the word "OK".

Or a light marker like yellow and a dark one, like red.

But again, you have a problem when you need two or more marks.


If you are marking with only one meaning, "to show where areas of interest" using red only is fine.

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