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