@Dan
Well, part of the point of the Mislow/Siegel paper is to say that "pseudoasymmetric center" shouldn't be used at all. It's old unofficial nomenclature that is better left forgotten. Much like taking "sterospecific" to mean "100% stereoselective".
According to them (and most modern stereochemistry textbook have adopted this view), you have to call such a center "stereogenic and achirotopic". For the purpose of this discussion, only the fact that it is a stereogenic (tetrahedral with four different substituents leading to local asymmetry) center is relevant (the fact that it is in an achiral environment, and thus achirotopic, is not really relevant here.) I don't know but I would think that if one wanted (I don't!), one could dig in the CIP nomenclature rules to potentially find a way to determine the R/S configuration of the blue center. If one wanted. As you mention, I think the more common treatment is to instead go for r/s.
Indeed, if you leave the original meso compound and go to the (R,R) or (S,S) compounds, the blue center becomes non-stereogenic (and as you've shown, "inverting" it doesn't lead to a different molecule) and you couldn't assign R or S. It also becomes chirotopic.
@orgopete
I wouldn't give too much thought as to the phrasing in the OP's post as he states that English is not his forte and also because a sentence such as "it is NOT a chiral centre only if the 2 chiral centre in red are both R or S" is a bit confusing. But yeah, (R,R) and (S,S) makes it a chiral molecule. However, the discussion in the OP's post was really about if the center was chiral or not, not the molecule.
Cheers!