While only the site devs can change the default color scheme, there are browser extensions that users can install to change how webpages appear on their local machines. For example, while I like the visual theme here overall, I use a Firefox extension called Stylish to increase the contrast between the colors for the visited- and not-visited question links on the main page.
I can put together a file in a minute or so that would change the colors of the text items you mentioned in your question and upload it to the Stylish site, where you could download and run it without too much trouble.
Stylish is available for Firefox (here) and Chrome (here).
Again, it only changes the appearance on the local machine. The Stack Exchange devs are the ones who could adjust the default color scheme.
Let me know if I can upload that file for you. Ciao.