I just tried something that I didn't have a whole lot of faith in. I bought some vintage linens that were yellow, especially where they had been folded. I soaked them in Wisk and Biz powdered stain remover for a day. Then I rinsed and soaked again the following day. There was still quite a bit of yellow,especially on one pillow case.So, I decided to try another method.  I rinsed the linens and put them on the lawn in the sun. The sun really did get the yellow out. Now I'm a believer in the sunshine cure. Hope this helps out someone with a similar situation. Make sure you turn the fabric inside out, especially if it has embroidery or an applique so it won't fade.