The problem might be strongly related to: markdown help page on meta.photo.SE is unreadable
If one goes to an anchor link that points to a section in the markdown help, the section's highlighting won't fade away completely. It does fade a little from more saturated yellow, but still leaves the text rather unreadable.
For example comment formatting:
… whereas code and preformatted text help (and only code and preformatted text section, it seems) fades away properly:
The problem occurs with Chrome, Safari, Firefox and Opera—at least.