Just the 'numbered' face of the leaf is in the 'white' on a good condition 1901 sight.
(I believe some Kragrifles, that were 'reconditioned' just before WW1, may have more of a homogeneous 'black-blue' appearance of the metal surfaces, but, the different component parts did not take this treatment evenly).
BTW - #0000 steel wool (or bronze wool) saturated with Hoppe's #9 solvent can remove surface rust from metal and leave blue and patina intact.
The edge of a copper penny or brass cartridge case, worked with a film of linseed oil, can be used to burnish and breakdown heavier rust deposits into a nice brown patina.
(Go slow, examine progress by wiping off the rusty slurry occasionally with paper-towel, and renew linseed oil. I do a final burnish with rottenstone in linseed oil and the edge of a popsicle stick. This can give a pleasant patina, but, will not remove rust pits).
Attachment 110456