The lightsabers in ANH were very hit and miss - Obi-Wan and Lukes' looked fine in the earlier scenes, but the Falcon scene has always been dodgy and the duel has a lot of 'problems'. I still think the DVD only made things worse - I happened to like that massively over exposed look that the lightsabers had. It made 'em look bright, unlike in Revenge of the Sith.
I never thought the colour in Luke's was 'faded', I just genuinely thought it was supposed to be closer to turqoise than Obi-Wan's. The slight difference was a good idea in my opinion. It's the same way that Vader's isn't actually red, it's got more magenta.