I don't have any thinner lighter cotton yarn to use. I have some dark sock yarn. That might work. The waste yarn I was using is much thicker than the yarn I'm knitting with. I haven't done the try on yet so I can look for other yarn. I'm knitting with sport weight and have the sleeves on heavy worsted. You are right that I should use something thinner if I need to get the needle in along with the waste yarn. I just figured I'd need the waste yarn a sufficiently different color so I could see it, and I don't really have that, and thinner, on hand just now.