I have noticed that the color of the clear film base (exposed portion of the film leader used to load film into camera) varies on E6 film, and that the lab always includes the leader ends. When I used to send out for slides, this would often be yellowish, or pink, or blue, or sometimes crystal clear. Now that I do my own home E6, I usually see the ends with a very slight grey (like a very light ND filter), or sometimes slightly bluish tint to the clear base. Is there any meaning/diagnostic value in these color variations, or are they simply a characteristic of the emulsion or base material itself?
I think the lab includes them for a more sensible reason, when they spool your film they put a code on it and the same code on the envelope, they include the leader to make sure they got the right envelope, and the tail to make sure they got all the images.