Use a dressmaker’s chalk for dark colored shirts and a dressmaker’s pen for light colored shirts.
Make sure that you are sewing the elastic over the line that you drew. Make sure that your thread color matches the shirt material.
Men’s large shirts work especially well for this.
Use a dress maker’s pen of light colored fabrics and a dress maker’s chalk for dark.
You can also hem the sleeves or armholes in a similar fashion.
For an interesting look, try a solid-colored shirt with pattered cotton for the skirt.
Use chalk for dark colored fabric and pen for light colored fabric.
If you are using stretchy fabric for the skirt, use a narrow zigzag stitch instead.
You will eventually be pulling these threads out, so the color does not matter. In fact, a contrasting color will help you find them later on.
