Swiss Streubel - Color Of The Silk Thread

I have a 15c rose streubel and I would like to have your opinion about the color of the silk thread.
The 2 possible colors are: green and blue.
The thread of my stamp is white ( snow white).
As you can see on the hereunder scan, a part of the thread is free and the other part is still embedded.
The free portion is absolutely snow white and the embedded part looks like to be white.

My question is : From the only 2 possible colors for that type of stamp( green and blue),is there one able to turn into white with the influence of aging and light ?
If you have already experienced that case, please give it !

Thank you

I found an older discussion about the color of the silk thread. Here is a link to the comments from one of our team:

https://goscf.com/t/27755#237997

It appears that washing with a mild bleach (or other chemicals) could remove all colors from the silk thread. Later in this same discussion is mention of using the cancel to better determine which stamp you have. Good luck.