I use spray to baste all projects and have never seen discoloration when I baste and set aside a project for what turns out to be some time. However, I never have left it unwashed in perpetuity, so I can't answer for sure. I spray the batting, not the quilt top/in this case handkerchiefs. That should lessen the direct spray on the handkerchiefs and in my mind the chance there would be discoloration over time.