I'm working in Pompeii right now and I've talked to some people there who are dealing with paintings. It seems, from what I hear, as if this report was based primarily on evidence from Herculaneum (which was exposed to much higher temperatures during the eruption of 79). So far everything seems good, you can actually see how some walls have changed color there. Pompeii is, however, another matter and most, the overwhelming majority actually, of the red walls there are, and have always been, red. We are, even in Herculaneum, dealing with a relatively small sample (I heard a figure of 50 walls, but I'm not sure where it came from) out of the many hundreds found.
Summa summarum; the reports title is rather catchy than correct. Yes, some red walls were yellow, especially in Herculaneum, but most were red.