The interwebs is full of examples (search for categorical color palette colour blind). But colorbrewer [1] is well known. And this [2] article "Color Universal Design (CUD) - How to make figures and presentations that are friendly to Colorblind people" gives loads more information.

[1] http://colorbrewer2.org/#type=qualitative&scheme=Paired&n=3

[2] http://jfly.uni-koeln.de/color/

Red and blue (like Jenkins, but that seems to be coincidental).

That said, if you think color accessibility is about picking the right categories of colors you have a long way to go.

The important thing is that the colors need to have sufficient contrast beyond mere hue. Light green and deep red is fine for me as a strong deutan (i.e. severely green blind) even though there are combinations of "red" and "green" that are practically indistinguishable for me.

Hmm, red-and blue makes sense, given that they are the furthest apart physically.

Obviously accessibility is about more than picking colors, but if a complaint is 'this is a bad color pair' it is interesting to know what is a better pair.

As for contrast beyond hue, does that include saturation? Because keeping luminance constant is an important part of keeping an interface legible.

I'd say a red-blue default with full configurability might be the best approach.

Red and blue are not ”the furthest apart”. Red and cyan, or blue and yellow, are complementary (180° separated on the color wheel). But color perception is more complicated than that.

I believe something like orangish red and bluish green are distinct enough to most people with a red-green deficiency (including myself). The difference in ”blue content” makes them distinguishable.

The actual wave-lengths are the furthest apart. Whilst that is not perceptually relevant, it is relevant to what happens when color-receptors fail. That is, as long as you have two different color receptors that respond differently to different wave-lengths, those will receive different signals from red and blue light.

The wavelengths that are furthest apart are red and violet. Which perceptually are close together, for red-green blind as well. But what does matter is picking the colors based on the corresponding receptors' peak sensitivity. The L receptors are most sensitive to red, and the S receptors to blue, so in that sense you're right. (Red-green blind or weak people lack the M receptors of have anomalous versions, respectively.)

Beyond what we traditionally think of as color blindness, there is an almost unlimited number of vision impairments your users may have that call for different colors, levels of contrast, and font size. To make software that is truly accessible to people with vision impairments, you need to make sure the user can create custom themes and that your software works well with screen readers.

About 1 in 4000 people has problems with blue and yellow. If you try to accommodate everyone, you just can't use color for information. I think using blue and yellow is a reasonable compromise.

White-on-black vs black-on-white should work, right? Though that would probably be less readable for other visual impairments.

There is none. The real answer is to always make the colours configurable. Red/green by default is fine.

Red-green color blindness affects 8% of males. Red/green by default can be annoying to the not insignificant amount of us who are affected.

You're just prompting the original question again.

Yellow is unreadable on a screen.

They used to make amber monitors alongside green ones. Yellow on white doesn't work, but why use a white background unless you're simulating paper?

I use both black on white and white on black. Usually, I find the latter enjoyable in the evening / night, but occasionally a bit depressing / oppressing during the day in my text editor. I guess it's also weird to have a bright room and a dark screen. But not in the terminal, where a black background always feels better for some reason.

So, why use a white background? Because it may feel better, and it may have nothing to do with paper.

Also, an objective reason: with black background in your text editor, it can be painful to switch to windows with a white background. If you try to set everything black background, you run into bugs: broken webpages, mails that set a white background anyway (bonus if they don't set the text color, or nothing is set but some words are highlighted or colored), documents, PDFs. I know because I tried. With support for dark themes in CSS it will probably improve but we are not there yet and you pretty much are in an unsupported territory.

The question also work in the opposite way: why use a dark background? Same answer: preference. For ecological reasons? It depends on the screen, and it should be measured especially if you compensate by setting the screen brightness higher.