[Uncle Bulgaria]

I very much doubt there will be such a code, as they are for digital colour matching. The dyes used in the manufacturing of the cloth will have been more variable, and probably related to a proportional recipe of chemicals rather than an absolute predetermined value.

If you want a colour code, one could be generated from a photograph but it will depend on the white balance, the lighting, the camera, screen etc. etc.

I think your best bet would be to replace it with something else (did you get a Ratchford sample card? They are quite helpful), or take the Japanese approach of making the repair obvious by specifically not matching it. It increases the visible expression of the object's history. While I understand it's not to everyone's taste, I personally think the attitude it demonstrates is quite admirable when dealing with old things that are used and express their wear and tear.