Whatever those other pages are obviously have lots of internet-power because this question keeps coming up, and we keep debunking it.
While some original paperwork made the suggestion of only two options, and other people have said the same thing, we've found over the years that there were Explorers out there with multiple colors not on that list.
Blue and Copper, Durango Tan, at least one of the Red colors (if not two), the aforementioned Chrome Yellow, and probably more.
Right here in this thread are at least three colors not on your list. All original Explorers.
In post #7 bchesley made an interesting comment about being able to order any normal color and then add the Explorer package just like any normal option. Makes sense, especially when given the facts of all the other colors.
Several threads here on classic pretty much confirm at least some of what has been mentioned in this thread.
Perhaps Ford originally intended to offer it as a special thing in only two colors, but as often happens customer demand, or perhaps cooler minds prevailing, changed their minds early on.
Either way, the rumors of only two colors being available have been greatly exaggerated.
Any sites that insists otherwise are wrong.
I know that's a bold statement (and bolder than I usually feel comfortable making) but at the very least we have documented several colors other than the expected two, from original owners, second-owners who bought when the trucks were young, and Marti Reports.
Paul