A dark slate gray might look nice.

Of the three I'd go with green.

I would choose the rust or black. The other colors add a stand out element that you might not want. Rust or black blend.

Rust or black but there must be some reason you don't want to use those so of the three colors you displayed I like the green or the red I guess.

I like the green best - the lighter colors seem to take the eye away from your ducks. It's going to be appreciated, no matter what.

What would no cornerstones look like on the outside border?

I like the green best.

Many thanks! This has been so helpful for me. OK - rust it is. I've already cut the sashing strips, so I need to use cornerstones. Plus I can't visualize the triple sashing without them. As I said, I'm colour and design challenged! Now to figure out a thin inner border to separate the rust cornerstones from the rust border. I might use a deeper blue as it is opposite orange on the colour wheel, and the rust is kind of orang-y. I'll post a pic in the pictures section when I'm done.

I know it takes more time but I like the idea of small 9 patch, it would really pull it together.

The rust looks good.