A decade or so ago, there was a lot of interest in this issue, and astronomers were perplexed that the white dwarf accompanying Sirius could have gone from a red giant to a white dwarf phase in only a few thousand years, leaving NO trace of any circumstellar gas behind. Usually, this evolutionary transition leads to a planetary nebula and expanding gas which lasts 10s of thousands of years. The 'red Sirius' mystery seems to have been resolved in a study of the literature during the Greek-Roman period in which the alleged 'red' moniker used to describe Sirius had nothing to do with its actual color, but with some other usage of the term 'red' that had other meanings at the time. I'm sorry to be so vague, but the bottom line is that the 'red Sirius' mystery is no longer a mystery to astronomers thanks to some sleuthing by historians familiar with the literature of the time when the 'red' term was first used to describe Sirius.