Hello oli1970, for me this is a later (the form for me does not conform to early WKC pieces) yellow trolon grip which was colored later on. When it was done and for what purpose I do not know.
But due to certain typical traces and a special feature of the color I personally think the coloring was done not too long ago with a black felt pen.
Just my opinion from these pics.
Regards,

1.JPG (42.68 KB, 140 downloads)
2.JPG (35.21 KB, 140 downloads)

wotan, gd.c-b#105

"Never look for sqare eggs" as a late owner of an original FHH-dagger used to say.