How to determine whether links have enough contrast?

I find it very hard to distinguish links from normal text on Programmers Stack Exchange, especially visited links on wall-of-text posts. The colour scheme used is:

Background    #fafafa (there's a background image, that's mostly #fafafa)
Normal text   #333333
Normal Link   #B64D27
Visited Link  #7F3A21

An example of a wall of text post is this answer, one of mine. When proofreading I couldn't see the (visited) link to the Wikipedia article on the first paragraph -- actually thought I forgot to add it!

Is it just me, or is this problem likely to be shared by a significant number of users? I have no idea how to approach this from a user experience perspective, proper lingo and all, I'm looking for answers that reference established practices and / or studies that shed light on whether the colors should be revised. I'll present those findings on Programmers meta.