A good place to start is here for consideration of various colors of silver.

It's no small matter that none of the parts mentioned are made of cast iron. The knuckles are steel forgings with a black oxide appearance, not any variation of silver or bare metal. New front end parts such as pictured show the color needed which is probably better done with actual black oxide or gun bluing than paint. Search You Tube videos for "black oxide", or you may try mixing paints in shades of black and dark gray. Black oxide resists red rust and is a viable finish coat if lightly greased or oiled periodically during engine oil changes. I use a brush and a 50-50 solution of Cosmoline and paint thinner.

Lower control arms are assemblies made mostly of press-formed steel sheet, but there are also forgings and rivets which are not all the same color. It's well known that lower control arms are mostly Cosmoline coated, and there are a lot of posts about that. Click on the special enhanced Google search box at the top of this page.

Upper control arms are wholly made of formed steel sheet in some shade of silver, and they will be in a dark place on a finished car. As Lilly says on his web site in the first sentence above, you should know that silver paints change their appearance depending on the amount of light. Therefore you should evaluate your paint tests in a light condition similar to how the part will be viewed in a finished car..

Save your Eastwood cast iron paint for your wheel cylinders and 4-speed case.