A "black painted bolt" may be from a Garandrefinished by the Greeks. They are famous for their"black" finishes on their M1903s & Garands. On the other hand, some veteran's groups painted the metal on their rifles gloss black to make them "pretty".
In any event, compare the bolts. If there is no excessive wear and if both head space, you have a complete spare bolt, not a bad thing. I have, on occasion, seen a firing pin break. So, a spare bolt can come in handy.