Anything lighter than black (and that's everything) will decrease the contrast* and is therefore less optimal.

The W3C has issued guidelines for contrasts on websites, to comply with:
Understanding SC 1.4.6

So if you want or need to use a color, then try these color-contrast checkers:

• https://contrastchecker.com
• https://webaim.org/resources/contrastchecker/
• https://snook.ca/technical/colour_contrast/colour.html

There are indeed many studies to back this up, and in some countries even rules to adhere to for governmental and institutional websites and screen applications !

* The only exclusion to the rule is bold bright yellow text on a black background.

Oorspronkelijk geplaatst op Quora: What is the best font color for text on a white background screen? Are there any studies to back this up in terms of optimal readability?"