But attire that is conspicuous in one border-crossing context for a user of a valid US diplomatic passport may not necessarily be conspicuous in another border-crossing context for a user of a valid US diplomatic passport.

Showing up even in beach shirt, shorts and sandals on a US diplomatic passport is not necessarily inexplicable; sometimes that beach attire is less conspicuous than showing up in business formal or business casual attire of the sort used at a DC/VA/MD government office/meeting in DC/VA/MD during the workweek. Avoiding conspicuous attire makes sense, but that requires first knowing what is conspicuous under which circumstances. It is not uniform.

Although showing up in a Speedo brief or bikini at an airport of entry/exit will certainly be uniformly conspicuous.

I've read the pages in it. It seems not much has changed.