I have red-green colorblindness. I don't really notice it, except on two occasions:
- When I see an Ishihara plate.
- When hyperlinks are styled using only a color that normal people have no trouble distinguishing from non-hyperlinked text, but which I do.
This isn't the biggest deal in the world, but it can be rather frustrating. Sometimes it is clear from the context where a hyperlink is, and all is well. Sometimes it is clear that there is a hyperlink, but unclear where it is; this requires a bit of searching. Sometimes none of this is true, and I have to hover over nearly every bit of text groping for possible links; that's annoying.
There are a couple ways this might be addressed. Different color schemes could be used, but there are other kinds of colorblindness that would need to be kept in mind, and so this solution is not very robust. Even better, some other kind of formatting could be added to links (e.g., underlining), or the link color could have a different intrinsic brightness from the main text (so even the totally colorblind could make out where the links were; I believe the TeX.SX Meta links are like this).