This will be a very, very casual jacket, really almost like a sweater because the fabric is so open and soft.
Been looking for a good linen or hemp for years. About four years ago, I saw some upholstery fabric from Cisco that seemed perfect. Kept looking around, since it was pretty expensive and I was naturally hesitant to use upholstery fabric for clothing. But I've never found anything I've liked nearly as much. Finally bought some to try. Mine's the second from the top in the middle stack. The color should be very versatile. I'd call it taupe, but it may be closer to what Manton's called "donkey" if I understood him (something between brown and gray with a little green). Color's a little more true in this pic:
They have lots of beautiful shades, weights, and weaves. And the company is really careful about environmental and social impact of their materials, a few more: