Red Cross 'Tracing Label' query

[Peter High]

A query has been sent to me as follows:

FRANCE-Tracing label 1939/45 Cover f.w. 50c x 2 adh. canc. **/** Signy-le-Abbayetown cachet-no dates.      Has in top left corner "C.C.F/2028" pinkish label and sent to"International?Red Cross PoW Agency in Geneva.
On back "?Wehrmacht Geoffnet" label code e {Frankfurt}
It is understood that there were different colours for labels for this tracing service.

Can anyone give any information about these labels please? Was the colour significant?

Thanks & regards,

Peter  :D