Yes I did the search, no I do not know what is correct. The finish chart that you can find on this web site is not clear what finish is on the upper control arm shaft. Is it 30% gloss? thought I read somewhere it was natural unpainted steel but have no idea where I came up with that. I finished media blasting all front suspension parts and have them in primer, waiting for the front end rebuild kit to show so I can make my car a roller again for the first time in over 17 years. I love the media blaster, from trashed to brand new in mere minutes.
Natural. You'll have to decide from a maintenance standpoint what to do from there. CastBlast or other faux paint. Or leave it natural and keep it treated.
I thought I read somewhere they were supposed to be natural but I keep finding conflicting info so I thought I would ask. Seems I see most of them painted black, I will most likely use the cast blast like my spindles, driveshaft, steering gear box and I think the steering linkage bars are natural also.
I would bet they are seen black because the subframe was painted assembled, or the owners did not know or care.