Color blindness and presentations

According to estimates from the Howard Hughes Medical Institute, somewhere around 7% of men and 0.4% of women are color blind. The most common is red-green color blindness. I always wondered whether the presentation rule of “never use red” in a presentation was true. So, I spent the a few hours on the website to find out. lets you upload images to see how they would appear with different types of color blindness.

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So, we can’t tell yellows from reds and greens, but we can still see the BOLD effect in the words clearly.

I decided to try a few of my own slides to see how they project:

These first two are from a lecture I developed before abandoning red altogether. I was very disappointed to find out my orange (2nd pic) suffered the same fate as red.

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Here is the effect in some of my more recent slides.

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So, the morale of the story is that it is likely better to just avoid red altogether, as well as green. However, they can be used with the following caveats:

  1. Do not try to contrast reds, yellows, and greens because they all look the same
  2. Consider using bold, italics, or other effects to give emphasis in addition to the color
  3. Used in isolation, a red or a green will appear yellow to a small portion of your audience. It will still stand out, just not the way you intended
  4. Checking your slides at a site like will avoid creating presentations that inadvertently diminish the learning of a portion of your audience


Howard Hughes Medical Institute (2005). Seeing, Hearing, and Smelling the World/Breaking the Code of Color: Color Blindness: More Prevalent Among Males.

The Magic Number 4?

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Another possible myth of presentation design is that the magic number for retention is:

7 +/- 2

It appears that the actual magical number is closer to 4.

A psychologist by the name of Alan Baddeley dug up the number ofter quote from the research paper by George Miller and actually found that it was a talk from a professional meeting, not research!

Baddeley did his own studies to support the number 4 as the true “magic” number for memory and information processing. However, this has not been studied extensively in medical education, especially with the ideas of organizing and anchoring.

So, for now, we can try to build our presentations around the number 4, but may be able to stretch this much further when other educational principles are applied.


Miller, G. (1956) “The magical number seven plus or minus two: Some limits on our capacity for processing information.” Psychological Review. 63:81-97

Baddeley A. (1994) “The magic number seven: Still magic after all these years?” Psychological Review. 101:353-6

The Truth about Serif vs San Serif Fonts…

I have long wondered about some of the “rules” of presentation design. One of them which I used to mention in my own classes was the classic Serif vs. Sans Serif debate.

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So according to Hoffman, et al. 2005, it turns out that the real key may be READABILITY. When asked about their preferences for projected fonts on screen, these were the top choices in order of preference. It is interesting that 3 of the 4 are, in fact, sans serif fonts, but don’t be so quick to throw out stylistic yet highly readable fonts like Times if they work for your presentation.


Hoffman B, White A, Aquino N. (2005) “Screen text readability: Ease, accuracy, and speed of some common computer typefaces.” IVLA Conference Proceedings

Exley K, Dennick R. (2009) Giving a lecture: From presenting to teaching. 2nd edition. New York, New York: Routledge