I was commenting about the earlier post's link having the (ordinary) passport cover's color appearing to be black (rather than blue), but that site having the color labeled as "blue" even as it appeared as black to my eyes.

US Diplomatic passport blanks' OFC and OBC color are not blue in color nowadays and generally haven't been for quite some. They are black OFC and OBC, as the latter post's link more correctly labels the color. But the link supplied for the non-Diplomatic book has the passport OFC appear more like black than blue to my eyes even as it's labeled the color as blue. [I've handled a whole variety of passports over the years.]

I would be surprised if the idea was to have US Diplomatic passport blanks issued with the same OFC and OBC color as the ordinary US passport blanks being used for passports being sought by most people in this thread -- no less so when the description details on the links have the right color labels for what has been traditional.

Black isn't blue to my eyes, but the links you supplied above seem to have black and blue as both looking the same to my eyes regardless of how they label the color. Does it look different to you in terms of the color of the outside covers?