Re: Hoth coat, we can conjecture back-and-forth what was seen throughout the 1980's (obviously actual film prints that cannot be replicated) and the merits of the various color timings of transfers to home entertainment versions over the years (which vary greatly in terms of coat color.)
What we do know for 100% certainty however is that both Kenner and LFL officlally endorsed the coat as blue back then. People seem to think it was one Kenner action figure - but it went way beyond that to other toys, comics and merchandise, all of it LFL officially approved. As we know from the stories of all the licensees who were rejected back then, LFL was every bit as picky and detail-oriented then as they were in the modern era. It's like saying they'd let ANH Han be released with a brown vest.
So this is not an issue of "some fans thought they saw..." and a "one-off mistake by Kenner" - it was indeed official and widespread. Now...
I will leave you with the most up-to-date official input on the matter, which I have posted before, from the Star Wars Costumes book, published a month or two ago:
"As a result of extensive postproduction color grading on Empire,
the anorak (coat) appeared to be navy on screen." - p79, Star Wars Costumes
So... coat costume WAS brown, but DID appear navy blue on screen. This... is official confirmation and supercedes any opinions expressed on any forum and ends the debate. Or does it?