Hunter Orange.

With gray siding, almost any color will work. I'm partial to red doors, but orange or yellow would provide a nice contrast too. Green would blend in with the foliage. A highly saturated blue or purple would add some contrast but not as much as the warmer hues.

Yellow

Tthe underside of portico should be the same as window trim.

The siding to the left of the house…what color is it? Is it the shadow making it darker?

If different from the house, paint the door that color.

What a gorgeous house! Look how great the color of that orange ladder looks down there. I'd do that.

Burnt orange

I'd pick my favorite color among the flowering shrubs/trees that you'll have. Do you know which plants you'll be including in your landscape plan? If not, I'd research the native and adapted plants for your USDA zone, see which ones you like the best, and pull a color from the prettiest blossom. :-)

Or, if you wanna take the easy way out, just do hunter orange.

Mustard

Match the trim color and let the landscaping provide the color. . . .This door doesn't seem like the street is close.

This house made me think of yours -

Can I ask how large you want the paperbark maples in that narrow planting bed to the left? " When mature, the paperbark maple grows to about 15 to 30 feet tall and wide, usually with an oval to a rounded oval shape. In rare instances, old trees may grow as high as 40 feet. This tree grows more slowly than many maples and may take 20 years to reach full height. Its slow-growing habit also means it can be a relatively expensive tree to purchase from garden centers. " Paperbark Maple Plant Profile

Thanks for all the great ideas! For those suggesting yellow, that was actually the builder's suggestion, too. Unfortunately, I just can't bring myself to do yellow, as it's one of my least favorite colors (I'm a pale redhead who looks positively ill in yellow, and I've never been able to warm to it).

I really like the idea of the red that RES shows, or possibly an orange. I'll get some sample cans this week and go from there. Right now it's a temp door and the hardwood isn't in, so I can try colors out pretty easily without worrying about getting paint anywhere I don't want it. That changes in about a week when they start the hardwood, though.

I do know the plants, but will have to dig out the list. They're a mix of native species designed to provide year-round interest and color. I know there are various color dogwoods in there and various tufty grasses, but I can't remember what else. I suspect that between the dogwood bark and the paperbark maples we'll have a variety of reds and oranges.

The siding is all the same color, just shadows making it look different. One siding color, one siding style, and one trim color. The underside of the portico will be stained cedar, though, which is a pretty common look around us (PNW) and is also used on other covered exterior spaces around the house. This was one thing about which the architect had pretty strong feelings, and we agree.

As for the trees, what to put there has been an ongoing debate. We considered lots of different options, but the Paperbark Maples won out because they should be hardy at our location/elevation, they provide winter interest via their bark, they're slow growing, and they're pretty readily available (and not cost prohibitive) around us. Our landscaper thought that while they can get larger than we'd want, the fact that they're slow growing will make it reasonable to manage keeping them the right size. That said, this is something we'll revisit with him before we plant. This has been a difficult area for which to pick trees.