Good comparison.
Personally I believe that the colour difference is a combination of age and material. The original silk ribbons were naturally a slightly creamy hue rather than the harsh brilliant white of modern materials. That's just the nature of undyed silk. Ribbons made from silk today have the same hue but with the edge difference.
Regardless of the shade, the edge appearance is a very good indicator with most medal ribbons as you pointed out. That is purely down to manufaturing technology and if repro / replacements cannot be made on old machinery they will look different!
Regards
Mark
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