@Axi2,
In the antiques fabric trade, the "patina" of white silks is well studied. Maybe you can find something re: fabric conservation at the WInterthur Museum Labs sites. SIlk will naturally yellow as a result of chemical reactions that occur in the protein structure. ALso, exposure to light can speed the whole process up. I do not believe that its reversble.
Ikat and silk painting with modern photo stable dyes will keep the colors vibrant longer but as for the white "ground", I dont think you can do anything to reverse it by much.
I used to do "picking" for antique silk ties and Id be careful about the color fastness/