This is my response, on the BCHF forum.:

Coloring the Truth: Sinaiticus

... There are a couple of problems with your theory of differing storage. which is similar to the grabbag of ideas that was thrown out in the British Library response.

1) the same distinction that exists today existed at the time the manuscript was published in 1862, and the ensuing decades, until today. This is clear from quotes from Uspensky, Scrivener, Dobschutz and others.

2) there is no reason to think that a supposedly heavily-used white parchment (unaged) manuscript would be heartily accepted as 4th century, an idea that was pushed very aggressively by Tischendorf. There is no other such white parchment ancient manuscript, (even more so when you consider the century-by-century heavy usage theorized) and ultimately that physical dissonance would be questioned as more rigorous examination insisted upon. (When Leipzig got close to doing planned material tests in April, 2015 on the German portion the idea was kaboshed before anything began.) At first, Tischendorf did not even directly link the two mss (see the Literary Churchman, July 16, 1859), however since they were contiguous text, they had to be connected. The shell game from that point on would be to emphasize the mass of the ms. in Russia, and later England, since that was "yellow with age".

3) while storage conditions could explain some degree of colouring, there is nothing known with storage that would go with the increasing stains that are in the coloured area. Other than something like a storm, of which there is no historical indication. There is no indication that Uncle Joe would take out the manuscript for his morning brew and vodka, with shaky hands.

4) there is no known distinction in storage conditions, that idea is all conjectural, and there is no history of anybody noting colour changes, either darkening or whitening

5) the evidence is strong that the British Library actually doctored the colour in the 2010 book. At that time nobody had publicly pointed out the distinction, clearly they were concerned to give an even colour appearance, since in a book the differences would be glaring (as they are in our combined photo).

6) the person who handled the manuscript created major fabrications and lies about the procurement and had a very checkered reputation. As an example, Baron von Bunsen is reported to have said "that man [Tischendorf] will do anything for money". We know of various ms. thefts by Tischendorf, including a leaf from the Archimedes Palimpsest and, apparently, a leaf from the Codex Ephraemi, and more. The Sinaiticus heists of 1844 and 1859 also have all the earmarks of theft. A paper by Natalie Tchemetska touches, a bit gingerly, on this theft problem. Beyond that, there are various suspicious circumstances in that era, such as the assertion from Hort in 1853 that "...Tischendorf will supply rich materials" and oddities in the papal visits. The vain-glorious self-promotion of Tischendorf was commented upon even by friends, e.g. Phillip Schaff, a textual supporter, referred to "his personal vanity and overfondness for his many and well-earned titles (covering ten lines on the title-pages of some of his books...)".

7) there would be an obvious motive to colour the manuscript. The official history is a pastiche of rather blatant fabrications (sometimes called myths, like the saved from burning and the red cloth), so when you reject the storyline that has no corroboration, you end up with lots of means, motive and opportunity. There was an unusual period where Tischendorf had full usage of the ms. in Cairo with two very lightly-identified Germans, who happened to know Greek.

8) the specific accusation was made at the time. And the person who made the accusations, Kallinikos, clearly knew Tischendorf and what had occurred at the monastery and pointed out the problems. He specifically highlighted that this colouring occurred. (Along with corroborating elements such as Tischendorf's bungling Greek speech, and the clear declaration, at an early day, that the pseudo-loan would never be returned, and the mangling of the ms, which matches the difference from what Uspensky saw to what was brought out.)

9) there are numerous, and totally independent of the colouring, compelling corroborative indications that the Sinaiticus ms was not a 4th-century creation. Including the Barnabas and Hermas textual "coincidence" histories of Simonides and the linguistic arguments of James Donaldson on those two texts. And there is no provenance for the manuscript before the 1840s, no monastery record, no catalog, no notice, no nuttin, poof provenance. And the arguments for authenticity are "soft", of the nature of .. "how could such and such accomplish this particular task and create that particular text." A variety of potential probative authenticity arguments, like the "ancient catalog", have poofed away. Oh, the evidences, including the Tischendorf family correspondence, clearly point to Simonides claiming involvement in the manuscript before it was known publicly, before the supposed red cloth discovery. Which acts as yet another singular powerful support of Simonides involvement in the creation of the ms.
This is being considered for tweaking and expansion to be used on the forum.