Who first proposed using a visual cue (of any kind) for hyperlinks the user has already visited? If the individual is not known, what hypertext viewer first offered this feature?
My guess would be NCSA Mosaic, but I cannot find confirmation of that. This article attempts to explain why hyperlinks default to blue in browsers, but does not explore why visited links are purple (or red, depending on your color spectrum sensitivity). Tim Berners-Lee and Ted Nelson say, at first, color wasn't used to indicate links at all (only underlines). The article doesn't touch on when a visual cue for a previously visited link was first offered.
When I think back on pre-WWW hypertext viewers (WinHelp, Hypercard, etc.), none I recall offered the concept of a browsing history, which would be necessary to support the concept of a visited link. Did the WWW introduce visited links to hypertext?