The pulleys and oil filler cap are steel so I understand that. The thermostat housing, timing cover and water pump are aluminum alloy(s) of some ilk. It was primarily those latter three that I was curious about why they turned out so dark.
This was pretty much the color of my timing cover (before and after I painted it).
https://www.ipdusa.com/products/2117...SABEgJ5pPD_BwE
However, I see that some covers do look darker
https://vp-autoparts.com/en/artiklar...vo-b18-20.html
Mine is an original Volvo cover that was machined to accept the later neoprene seal.