The first paper from the Hyperties group cited (https://www.gwern.net/docs/design/1986-koved.pdf) does not cover color at all. It does mention some user-testing. I checked all the papers in _Hypertext on Hypertext_ and none mention Hyperties or color in any major way. (The keynote is a good read, incidentally: https://www.gwern.net/docs/design/1988-vandam.pdf ) If you look at the Berners-Lee document cited, the Hyperties mention is buried in the bibliography; it is not even cited in the main text nor is Hyperties or link coloring mentioned, so I'm not sure why it's there at all, but it sounds like one of those cites-just-to-be-comprehensive, which often mean the author has never read the citation in question - so based on that, I'm unsure that way over in Europe Berners-Lee read any of the papers, much less actually saw the disk in action. The historical Hyperties page includes videos which show that by the time of the disk, they had defaulted to blue for link coloring, and mentions testing 3 colors (red was also used in Hyperties for other interface parts, so obviously they tested red vs blue vs ???). But the Hyperties papers after that do not mention color anywhere either. In fact, I can't find any Hyperties publication at all which reports the color usertesting or even that the results favored blue. It seems you just had to look at _Hypertext on Hypertext_ and assume that they picked blue because it was good?
So, checking OP's references, I think Berners-Lee may never have seen _Hypertext on Hypertext_ (at least, in computer form); and if he had, he would not have known the blue was the result of user testing (because nothing in it says so); and if he had both seen & deduced that, he may not have both remembered & cared years later when setting up his own browser defaults for color monitors, and he doesn't say so anywhere.