If you are worried about colour fastness, make a few stitches on a piece of scrap white fabric. Moisten a paper tissue and dab the stitches. If any colour comes off onto the tissue, you have your answer! Either wash the thread and risk losing the original shade, or make sure your hands and work area are pristine throughout your project.
i use sometimes the silk floss, is really soft in touch, and really pretty colors, i see only one problem, the dark color could loss and dye the fabric, and for the girl who wash the work after, must to wash the silk before use,or all the fabric (fiish work) coul be a disaster.