I use silk thread too (YLI 100 weight), but I've only found a good selection of it on the internet, or occasionally at quilt shows. Nancy Chong, of Pacific Rim Quilt Company (Hawaiian quilts) uses 50 weight Aurifil cotton thread, and she does superb applique. If you were making a Baltimore Album quilt to show in a big quilt show, I would say always match the thread color to the top piece, but for a child's quilt that will be used, that just isn't necessary. Be sure to post the quilt when you're done!