I have used Kona Cotton for over I think twenty years. I never have noticed any spotting when steaming it with my iron nor do I prewash. I have bought my Kona cotton at quilts stores and JAF. JAF may be second quality fabric but quilt stores only buy directly from Robert Kaufman which is 1st quality. You can always go on their website and send them an e-mail about your concern. I have seen some nice comments on Moda's solid line. You might check into that fabric to make sure your customer is totally satisfied. Good Luck !!