Black will blend. The silver will stand out.
Can you take a photo and photo shop it .
Living in New England many homes do a monotone look where everything is the same color and the landscaping stands out. The lighter you go the more prominent it will be.
Take into account roof color, trim color, deck color too.
Do you need to worry about heat?

Thanks for the response. I was looking at the house again today, and I totally agree the silver will pop and the black will blend.

We live in northern-ish prairie Canada - long cold winters and short summers (but the summers can get hot for sure; 90 degrees is not crazy in the summer, but we would never have more than 2 or 3 days in row of that temp before it cooled a bit).

Roof is extremely low slope, so you can't really see it, but it is black. As I said, the window trim and door trim on the front is all silver, soffits are cedar and fascia is black. Deck is all poured concrete (ie. gray).

I am leaning towards black...thoughts?

I had replaced a rear wrap around deck and choose white rails due to the home trim being white . There was a balance.
I have learned over the years that you need to take into account what is near and beyond the project.
I am in the middle of a pool build and the husband wants white fencing whereas I say black cause the white will stand out and you see past the black.... a trick on the eyes.
I am not a designer thus why I say take a photo of the home and draw in the silver rail & posts.
Black will heat in the summer . Will it be hot to touch?
At night will it be a safety issue since you can not see it at night? Will you cap the posts with lights?

The home network recently aired a home redo in Decatur , Georgia where they painted the home black and installed a white railed two story porch. It looked fantastic. There was a balance....

Your stucco, door, window trim and walkway are silver/grey.
The soffits are brown
The fascia and roof are black.
Could you post a photo ?
You need to think about balance. At first I thought black too .
I would do silver to blend in with the stucco and front door.

Could you post a photo so others could chime in ?
Think of this as a scottish plaid. A plaid has three to four colors and when you add the right balance it makes some colors stand out and others compete. You need to look at the color and percentages of color.
As I composed this I have vacillated between the two colors. Most homes have three colors....... when designing a room you also have three colors in percentages.

I think you should do the silver/grey rail and paint the front door a peach , orange , blue or even violet.
Or you can add hard scape in that color.

If you do black in front of the stucco grey your eye will stop at the black rail and not be fooled.
I hope I am giving you ideas.
could you do a photo?

......