Forget about what things look like on film, the color of lighting, the color grading.
I work in the film industry the idea of making a brown coat with the expectation of it coming out blue with lighting is just nonsense.
Just acknowledge the physical evidence:
(A) McQuarrie drew a blue coat.
(B) ILM made a blue coat for the animatronic miniature.
(C) The actual coat still has blue residue on it although it is now generally medium brown after decades, it was never the current shade of brown in the movies incidentally. So it was dyed one way or another.
End of story.
I respect your opinion, and since you would like "facts" here are a few:
1. I have seen the coat multiple times in person, and even handled the coat on several occasions. Once in 1994, 2001, 2006 most recently in 2010. The color has always been the same.
2. LFL Archives has stated on numerous occasions that the jacket (which was custom made) has always been brown from first day on set to end of production
3. LFL Books in conjunction with Brandon Alinger just released a book detailing the costumes of the original trilogy......in that book the jacket is featured full spread with the same information regarding its color, and the reason that the jacket appears blue on screen. As someone who works in the industry you understand gel lighting and its affects on wardrobe.
4. Per Phil Tippet himself.........to his knowledge the coat was made in blue to match the dailies that were being used to assist the stop motion process.
5. There is NO blue dye in the seams of the jacket, and there are no indications of the jacket having been any other color than brown in person.
6. LFL ESB wardrobe records clearly marked Han Solo's jacket as brown.
Now these are indeed "facts" and are not personal interpretations of any fans. If this is not enough fact then no amount will be.
I am not trying to convince you in anyway, but you asked for facts. Have you actually seen the jacket in person? If so then there would be no confusion as to what color it was made from/ and still is.