Mark - At least you could start a fire with your string....
I also really like linen.
B-50 is available in tan colour I think for that 'natural' look!
I've made yucca strings and apart from the extra weight they are pretty good.
I've also made nettle strings but give yourself plenty of time to process them. You really need to get them so there is NO green material left. The fibers themselves are pure white.
Sinew makes a great string once you get the hang of it.
I must say though I always fall back on dyneema if I want top speed. 4 strands on a 60lb'er sings a bit but boy do the arrows fly!