Double black Retzuas
In the recent years, double black retzuas has become rather popular. Apparently it answers to the problem of retzuas becoming posul through peeling paint etc... The Rambam writes that the noi of the Tefillin is to be completely black on all sides, although the Mishna Berura 33:21 writes that we are not nohag like the Rambam in this. The Shavet Halevi 9:16 writes that this is not even a hidur since the Gedoli Yisroel never wrote (or had for themselves)for the need of double black retzuas. He also brings that this is the opinion of The Shulchan Aruch HaRav by only mentioning that it should be black mibachutz. Although the shavet Halevi does conclude that if yechidim do it for themselves and not as a horah - tavo aleihem bracha. My questions are the following, when did the double black retzuas start most recently? Have the Rabbanim seemed to change their opinion on double black retzuas or is this recent trend have more to do with the market which not necessarily know much better? Appreciate your input.