Since most people associate blue words/phrases on a webpage with hyperlinks, I know it's a bad idea to use blue text to provide emphasis on a word or phrase within a paragraph. However, does the same issue apply when blue is used for headings?
I definitely agree with the previous statements regarding the need to be careful to not cause confusion about what is/is not a link. However, from a strictly accessibility standpoint, you would be best to focus on the contrast of the heading more so than the blue/not blue. To check to see if you have adequate contrast in place, you should check WEB AIM's Contrast Checker.
From the Smashing Magazine article 10 Useful Usability Findings and Guidelines:
Blue Is The Best Color For Links
While giving your website a unique design is great, when it comes to usability, doing what everyone else is doing is best. Follow conventions, because when people visit a new website, the first place they look for things are in the places where they found them on most other websites; they tap into their experience to make sense of this new content. This is known as usage patterns. People expect certain things to be the same, such as link colors, the location of the website’s logo, the behavior of tabbed navigation and so on.
"Google keeps all links on its websites blue for a reason: the color is familiar to most users, which makes it easy to locate."
- If its a hyperlink headline of an article I would use the blue text color since you are trying to get people to click on it.
- If its just a simple headline for a page or its best to use a non-distracting color like grey for example.
Headlines are used to get your attention but if your goal is to have the user continue reading the rest of the page it should not be the focal point and blue tends to do that.
Again it depends on what is used for and the type of site it is.