There are several items of head-canon that I had about Star Wars as a child, and which I carry to some extent to this day. Most have been shown demonstrably wrong by various episodes of the movies. I have almost no exposure to the Expanded Universe or even the animated series.

Light Sabers

To me lightsabers are a Jedi weapon and the blade is a focused manifestation of the Force. As such the color is personal to the Jedi weilding the lightsaber. It is their aura color if you will.

This idea was somewhat damaged as early as Empire when Han uses Luke’s to slice open the tauntaun, but I just told myself that the force was strong with Han and he’s just in denial. It would help explain his skill as a pilot and his general luck.

Span of the Empire

From Obi-Wan’s early tales of Anakin and himself fighting in the Clone Wars to Grand Moff Tarkin laughing at Vader’s hokey religion, I always felt that time scale was much more epic. Hundreds of years of Empire rule had passed. Obi-Wan is a Jedi and Yoda is 900 years old, so it’s easy to believe that he is talking about something that happened hundreds of years ago, not just 20. Too much in episodes 4-6 doesn’t make sense if the Republic fell 20 years ago.