I've been playing with bits of fabric and the sharpies. I don't like the effect of drawing directly on to the fabric with the sharpie, it leaves the obvious lines and looks like a childs drawing. I prefer a more subtle blended look. So instead I put patches of colour from the sharpies by scribbling on BAKING PAPER - the ink sort of scrunches up and looks like it is fading, but hang in there it leaves plenty of colour on the paper. I put the paper on a plastic tray (or something you don't care is going to get messy) The I lay the silk on top of the coloured baking paper and then drip rubbing alcohol on to the fabric. The colour comes up through the fabric (with a bit of poking with the end of a pen) and bleeds out and makes nice subtle patterns. Hang it up to dry (quite quickly as it is alcohol!) The Sharpies AND the rubbing alcohol smell A LOT!!!! So use in a well ventilated area and don't try it if you have a headache coming on.
I'm sure there may be other ways to get the colour on to the fabric, this is just the one I stumbled on that worked for me.
Interesting technique! I might have to give this a try.