IIRC the original screws should be plated. You can remove the plating and then polish the screw heads in some sort of spinning arrangement such as a lathe or drill motor with some abrasive cloth or sandpaper.
However the resulting circular polishing marks are unsightly to some, so the screw heads need to be final-polished in a direction that leaves all remaining polishing marks parallel to the screwdriver slot.
After final polishing, I've found that Oxpho-Blue Gel is quite effective at recoloring to a nice rather dull blue but it takes 3-4 applications with THOROUGH degreasing between applications as well as applying it using DEGREASED fine steel wool.
Regards, Joe