But even in the original unaltered DVDs his coat looks blue.
I really don't know enough about it, but I believe the "unaltered" DVDs are not what was seen on screen in 1980. I believe ESB Vader's saber is pink on both DVD versions. I'd have to poke around on the revisited forums for the right info.
EDIT: The original theatrical versions were NEVER released on DVD. The ^^^^ commonly know as GOUT are NOT the theatrical versions. They are the "definitive collection" masters transferred to a incredibly BAD looking video.
The differences between the theatrical versions :
1) The colors are different on many scenes - just look at the Tantive IV segment on E4 (the walls, the rebels shirts) or the blue snow on E5. I don't know if these are color anomalies created by the film aging, or "deliberate creative decisions", but they were NOT on the original movies, just look some older laserdisc or VHS transfers.
2) The digital video noise reduction which was done to this masters ^^^^ed the complete video, now we have a video with a very small detail, trails, 4-eyed stormtroopers and similar ^^^^ which was not on the original film.
3) Some frames are missing
4) The audio is NOT from the theatrical versions, it is from the DE version. It is VERY similar to the theatrical stereo, but not the same.
5) At some countries (like Austria) the audio suffers from PAL speedup.