And the winner is.....
This is the same yarn as in the rest of the sweater, Louisa Harding Willow Tweed. This is color #01 - Natural. Now, if I'd had this yarn in my stash to begin with there would have been no problem with deciding.
The first decision I made was to use an off-white color for the minor stripes. White would have been too stark a contrast (I agree with you Barb B). I thought of medium-colored stripes but I liked the idea of keeping the entire project in a lighter color combination.
I shopped my stash and did find some off-white in a DK weight but it looked heavier than the Louisa Harding yarn. I've been doing gauge swatches and the yarn seems closer to a sport weight. Using the same yarn will ensure that the weight of the yarn is consistent.
So, the decision was made to buy yarn even though I'm planning to use the yarns I have in my stash for the foreseeable future. The color is right, the weight is right and I won't need much since it's a small part of the design. The yarn is discontinued and in short supply, especially in this shade and I wasn't seeing it anywhere. Then, I thought of eBay and found what I needed. In the meantime, I have plenty of other projects on the needles and in the offing. Next time I'll tell you about the stash-busting project I've just started.