The many different paint schemes allow the railfan to know when the CN Locomotive was last serviced and modified. That helps a lot.
Andrew
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It's simply because CN has higher spending priorities than repainting.
As such, although the railroad may have a single "corporate standard" paint scheme at a given time, it can take *a while* to accomplish unity. CN is not alone, viz CP which not only has a couple of CP proper schemes running around, but units still with MILW black beard and SOO paint to boot.
This phenomenon is not unique to RR's; many airlines will have planes in >1 scheme flying around for several years as they phase in the new image.
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