Impulse Records spine colors? Orange/Pink/Red?

I have found various discussions regarding the Impulse Records label discography and the differences between original and reissue copies of these records, but none of the discussions speak of the difference in the colors on the spine of the gatefold. I have several glossy, orange/black RVG, etc. records that I would consider "original" issues but noticed that the color of the orange on the spine varies from album to album. Some are more orange, some more red, some a lighter pink...Can anyone speak to the differences in these
Do yourself a huge favor and buy a Goldmine Jazz book. They go into great detail about record label colors and details, as well as info on which Gatefold is the original, etc.

It also has details about the Goldmine Grading system, which has been the standard in record grading for years.

It is a wonderful resource.
Brianw has a good answer but it could also be sun damage
Thanks for the advice. I will definately pick one of those up.