I have a German K98k, the bluing they used is pretty good, nearly 80 years later and only a few scratches show that it had been used extensively. I tried cold & hot bluing myself but never got even close to the quality of said bluing, it would always scratch terribly, so I always leave the bolts of my builds in the white.

The thinking behind it was mostly corrosion resistance. The German WW1 Gewehr 98 had actions and bolts in the white, but even at the very end of their production they started bluing bolt and receiver. Later in the 1920's the G98 rifles were converted to the Reichswehr Gewehr pattern, they got new sights and all blued bolt and receiver.

Having said that my builds have bolts in the white, I always give them a satin finish to remove glare. I take the rough side of a dish sponge and carefully run it in circles over the bolt and Mauser extractor, that will remove glare and make it look like satin stainless. It does not mess with the smoothness of the bolt travel at all and looks quite good. ( - I also did that to the brass receiver of my 44-40 Uberti lever action rifle, it looks so much better now than with that factory mirror-like finish.)

Here the original blued K98k bolt next to a CZ 602 bolt: