I've noticed that developed colour negatives usually have an orange layer.
Is this an artifact of an old printing process, required by the chemistry, or is there some other benefit to it?
Looks like photo.net has a really complete answer:
Why do negatives need an orange mask? The simple answer is "impure dyes." This is generally true of all chromogenic photographic materials, where the dye molecules are made of a color coupler that is built into the emulsion, combined with the by-product of the development of silver by a color developing agent. With this kind of thing going on, the choice of dyes is a bit limited, and we end with dyes that are not as good as some others... (more)