Just to provide some additional examples and similar but somewhat different lighting and camera settings.
Freshly cleaned 69 spindle (small suspension) before it was restored and reoiled. At this point the cast finish is very flat and chalky so when oiled or coated the cast will darken somewhat and the contrast between that surface and the machine surface will increase
A NOS example - Still has a protecting coating/oil/wax that will darken the flat quenched finish like the ones installed on the assembly line would have had
And an original big suspension spindle on an unrestored car
Hope these all help explain what we're attempting to describe and help others going through the same challenges as you are
Helps allot that things don't rust as badly here locally