Aww shucks Caitlin
The Kaygee thread does come in many colours beige brown green red - pretty much anything you would want to use.
My comment which mentioned silk - was as Caitlin interpreted - you can use silk - or rayon or nylon or cotton or whatever - its not the material thats key to hidden knots - its purely a technique.
The only reason I am "cagey" when it comes to certain techniques - is that I had to learn these the hard way, ie trial and error (sometimes lots of error) - even had close colleagues slam the door on sharing the inner secrets of knotting. (Yes I am slightly bitter and twisted

but dont hold that against me) Maybe one day when I am not working commercially I'll spill my guts on techniques - or perhaps you can trick me into it on here
One supplier you may want to try for Kaygee thread and I have no relationship with them except as a customer - is benjaminscrafts (Australian based) . They do have a web site.
Regards
Bernadette