I'm not entirely sure on this but there was something on this post: http://originaltrilogy.com/forum/topic.cfm/Harmys-STAR-WARS-Despecialized-Edition-HD-REMASTERED-is-now-officially-released/post/557865/#TopicPost557865
Mverta was talking about the bulbs used when this was being projected and that a bulb from the 70s had a warmer yellow hue to it.