If you can not decide I would interpret that to mean that both choices hold an equal value to you. If that is true than I would say flip a coin.

The range of difference is already extremely small and the choice is subjective and may change because of any number of factors such as other elements like shutter or door colors or time of day or year or anyone's mood at the time.

I think that the darker will give it a tiny bit of a newer striking look and the lighter will give it a tiny bit more of an aged mellow look.

I had the same thought as Virgil and in the same order!

Virgil is correct on all counts. Gray, unless you're talking plain galvanized steel, isn't a farmhouse color.

I suppose it has to do with ones view of what a "farmhouse" is.

When I Google Farmhouse pictures I would say about 90% or more have grey roofs. Yes, many are metal but grey just the same.

However I do like red and green also. I think those are bolder choices which would give it more distinction.

Red and green asphalt shingles were traditionally cheap roofing materials and, thus, frequently used for barns and other utilitarian buildings as the least expensive way to roof a building in many parts of the U.S.

Corrugated galvanized sheet metal panels became commonly used as inexpensive siding and also for inexpensive roofing for utilitarian buildings in many parts of the world.

Crimped and standing rib metal panels, in a wide range of finishes from simple galvanized to on-site painting to factory baked enamel, were developed for more durable and longer lasting, albeit more expensive and sophisticated roofing options.

All of these have a simple and utilitarian look to them, suitable for houses that are straight forward and unaffected, as a true farmhouse is.

Good luck with your project.

Just plain galvalume metal would be my vote.

Reconsider dark green. Lovely on a white farm house.

I'm always partial to a red roof on a white house with a red barn the same color as the roof out back. That just says farmhouse. On the other hand, all of the local historic 1800 Southern farmhouses are all white with green roofs and green shutters to match. Usually with a black door. The 1850 brick plantation house where I recently attended a wedding had plain galvalume. Not sure what it had originally, but the roof was from the 60's. The modern additions also used that to tie them together.