A while ago ... well, several years ago when I started quilting, I ran short of white cotton to finish a wall hanging and finished it up with a white poly/cotton I had on hand. Over the years, the p/c has turned a nasty shade of tan and it is right next to the 100% cotton. Every time I see it, I say to my self ... see, that's why we use 100% cotton! I don't know how black p/c will age but the choice is up to you. If your quilt will not be exposed to a lot of sun light, the chances of fading won't be as great. LOL