Felt fabrics of different colors are available at textile wholesale shops. These are washable so can be used to make design your own t shirts. make colorful, interesting patches and sew it on your t shirt, like i did it on a bright yellow t shirt. I first painted the tee with fabric colors and then stitched the patch on it. you need to first paste the patch with fabric glue so that while sewing it doesn't move from its place.