It might just be oil blacked Walnut Jim, I've a forend from a similar ex Indian No4, with the typical Ishapore screw and that is black as night on outside, normal colour inside....
I would photograph it if I could remember we're the hell I put it!
It has to be said, many of these ex Indian No4/5 rifles are 'very' well used.
So do please check carefully before shooting.