Sometimes colors are printed into the fabric and these can be quilted without problems. Other times the design is stamped on with a rubbery substance. Do NOT quilt over this. The needle hole may cause the design to peel off the shirt. Just quilt as close to the design as possible. The top left block, the rose love, and the "theta to the rescue" blocks are examples of shirts handled in this manner.
|Baylor University Theta|
Because of large, irregular unquilted areas, I prefer an 80-20 (cotton/polyester ratio) batt for t-shirt quilts. I use regular sewing cotton thread (40-50 weight) or nylon monofilament. I think a size 80/12 or 90/14 universal needle works best on this combination of knit and woven materials.
I linked up with the Free Motion Quilting project.
Fret not; enjoy the day.