I have used multi-strands of materials for both the top and bottom on some patterns such as my Peeping Caddis.
That pattern I used 8 strands of flat-waxed nylon for the top and 4 for the bottom.
By using multi strand so different color flosses your get variegation during the weaving process.
Adding a single strand of blending filament or crystal flash you can get ever so many variations to the theme where no two will be the same.
I have been using some of the three-strand silk yarn and variegated yarn out of it by unfurling it replacing the segments with different colors and retwining it.