Yes, the colors for the HNQ have changed. But visited and unvisited links are different colors for me on main, so I need to ask: Have you clicked any of those links?
I checked the Wayback Machine for August 16 on the main site and it shows this:
This isn't a particular surprise, since it was announced ages ago that there would be changes to themes (among other things) across the network.
Currently (on the main site) I see this unvisited links in the HNQ as #333 (which is the same as #333333) and visited links as #555 (again, aka #555555), same as MetaEd. These colors are the same colors that are used for question titles (e.g. on the main page):
(In case you don't have superhuman vision, the top one was visited.)
On Meta, I see both visited and unvisited HNQ links as #0C0D0E. (Actually, like main, titles links are also this color):
I think the HNQ links might be the same color on all metas, actually.
This really needs to be changed.
While I'm mentioning changes in link colors, I'll also state that I just noticed (on both meta and main) that the preview (e.g. of an answer you're composing) now shows a difference between visited and unvisited links like so:
(This is probably a good change.)