I read a newsletter today that warned website customers of “going grey.” Then she linked to a website of an example of both grey text and black text next to each other. Here’s the link to the examples: http://andesandassociates.com/Gray_Font_vs.html.
A person’s eye does a Funny Funny thing at times. When it sees a darker color next to a lighter color, depending on the shade, it’ll offset the lighter color to appear even lighter and the darker color to appear dominant. Which, black is dominant over grey, sure, but a better plan would have been to provide to different pages–one page with all black text and one page with all grey text.
I’ve maintained sites with thousands of users and trust me, I get complaints when the font contrast is too high. And then I get complaints when the font goes grey. Basically the point is, users will complain.
In looking at the example, it is rare that a skilled designer is going to go that light with their fonts–not on a white background. A more appropriate example of a color to choose would have likely been: #333333. It is more common to see the black font slightly offset. It breaks the contrast up a bit more so its not as sharp to the eye.
And on a black background, its not uncommon to use a slightly grey (more not-white than grey) color. No one’s going to choose the a grey color that’s too close to the actual website, unless its being placed in a non-important area primarily designed to attract robots.
If you really want to have a hard-to-read-site, however, go for it. Just provide a “print” css file so that the visitors who don’t leave your site and print it instead can actually read the text once printed.