I'm colorblind and have difficulty seeing red hues. Certain colors, such as red and green (LED indicator lights on a modem), brown and either green or red, and (less frequently) blue and purple, are hard for me to tell apart. Generally speaking, reds appear dark to me; a cranberry or crimson is more obviously red (and thus more obviously not black) than a cherry or burgundy.
For example, consider this image:
In figure F, the wide horizontal HSV bar (right side, second from the top), the region of the right (red) end comprised of the bottom 60% to the right of the 3 in the caption appears entirely black to me. The left side of this bar is marginally worse, but more difficult to describe, and I don't have access to an image editor.
In figure H (bottom right corner), everything appears black below the V on the left axis and to the left of the right edge of the equals sign on top. The next portion up, to the top of the V, isn't black to me, but it's only easily discernable because the image is a color spectrum. If it were text that color on a bright, high contrast background, I'd have trouble immediately telling the difference between it and pain black text.
I find it very difficult to tell on the mobile site theme when standard text in a post's body is a link, as the red [? :(] link color appears quite similar to the black text color to me. If it's not obvious from the context what text is linked, but is obvious that there should be a link somewhere, I often and easily get confused. If a post's text doesn't immediately suggest a link, I'm surprised if I end up accidentally clicking one. I have checked this on SO, DBA, and skeptics, with both stock and Chrome browsers (Galaxy S3, Android 4.1). I have also tried every different level of screen brightness, but to no avail. However, here on meta the links are green and don't give me trouble.
The color for visited links isn't as bad, though it doesn't really pop off of the page for me either, because it's brighter (greener in RGB). Most of the time it's not really difficult for me to tell when post text links somewhere I've already been, though this may well have to do with the fact that I've already clicked through, and so know there's a link there in advance without observing the color, potentially skewing my perceptions further.
Upping the "brightness" of the link colors (V/L in the HS* spaces) or adding a color independent cue would greatly improve my ability to detect links when browsing on mobile.
Here's an example, from this question on SO, where the word "this" in the first sentence of the post body is a link (I wasn't able to tell whether the linked text was "this" or "this link" until after visiting):