Dyeing imperfections that appear as white specks on cotton fabrics that have been dyed deep shades are a major problem in the textile industry. The presence of these imperfections in raw cotton is not evident since they only show up after dyeing. Processing through fabric dyeing results in both time and product losses when white specks are present. Approaches for eliminating or minimizing the problem include plant breeding, changes in growing and harvesting procedures, and additional finishing during dyeing. None of these provide immediate cost free solutions. A method of screening samples for dye defect potential before processing would allow mills to divert affected cotton batches to non-problem products. In this paper, a simple light microscopy process is described for screening undyed fabrics, yarns, and sliver. This darkfield procedure discriminates between common fiber tangle neps that are not dye resistant, and those that consist of bundles of extremely thin-walled fibers that will not dye.