Summary: Instead of using \textcolor{red}, green, and blue, use purple, teal, and blue. Want more colors? Use \usepackage{ninecolors}.

Which default LaTeX colors are readable?

The set of LaTeX default colors are chosen primarily to be a mathematically clean subsample of the RGB space. For example, red, green, and blue are just #FF0000, #00FF00, and #0000FF—the codes look nice, but the actual colors have drastically different brightnesses ■■■. This leads to some unintuitive behavior, like \textcolor{green} making text pretty unreadable. (See this example?)

I wanted to find some simple-to-state advice for what to use instead, so I went through the list of default colors and checked which met the web standard for being readable against a white page. (See the tables at the bottom for more specifics, and additional data for dvipsnames colors.)

6 meet this standard for use as text color against a white background: blue, purple, teal, violet, black, and darkgray. Note that red is not on this list! I think this makes sense: I often see default red in papers, but it is bright to the point that it slightly hurts readability, at least for me. (See this example?)

So, in short, you only wanted to use default colors, purple, teal, and blue would serve as good replacements for a red, green, and blue.

Other color advice

Here’s some other general strategies I use to pick colors for talks/papers.

ninecolors package

In 2021, the ninecolors TeX package was released. It defines reasonable defaults for color choices (for example, here are their colors red4, green4, and blue4), and I’ve used it for papers ever since. Recommend.

Steal colors from data visualization software

If I need more than one color, I often just copy existing sets of colors from matplotlib, Tableau, Excel. They’ve already done all of the hard work of making colors look nice together while also making colors maximally distinguishable, even for colorblind viewers. This sort of software also often has excellent documentation about how to use colors in plots and things.

Don’t steal color schemes from text editors

Once, I gave a talk using the solarized dark theme, and then someone later told me that the slides were very hard to read. Since then, I’ve heard other people make this exact mistake as well. And I think it’s quite a bad mistake: even if everyone can technically make out the text on the slides if they try, once someone in the back starts daydreaming, you will not get them back unless your slide is immediately legible at a glance.

Coding color schemes are often designed to have less contrast between light and dark. This means that they’re harder to read. And for talk slides in particular, you want your text to be easily readable, even for those sitting in the back, and for those with weaker eyesight. (And I think generally “light mode” is preferred over “dark mode”, since the former projects better across various lighting conditions.)

Don’t rely on color too much

As a final comment on accessibility, I want to point out the guideline that no crucial information should be communicated solely through color. I highlight important things with colors all the time. But I try to follow the guideline that, if my document was printed in grayscale, someone could still understand it.

Appendix: methodology and data

There’s accessibility guidelines for how large the contrast of text needs to be against its background. It’s designed for the web, but since pdfs are typically viewed on screens, I used it as the standard.

What these guidelines give is a formula to measure the relative luminance of the two colors, and then measure the relative contrast between them. If the contrast is above 4.5 to 1, it meets the minimum bar for being used for body text.

There are 19 default LaTeX colors. I used a color checker to check the contrast.

And here are the colors named by dvips, sorted by contrast.

Bolded are the ones that meet the contrast guidelines against a white background. Overall, the colors that remain are pretty unsatisfying: for example, there’s only one green. This is why I was so happy to see the ninecolors package when it came out; it is much more usable as a set of colors than any other package I am familiar with.