Dye-Lishus® cotton is scoured and mordanted in the fiber form, before it is carded and spun, which means I can blend it with untreated cotton to make yarn, or I can mix it with untreated yarn to make fabric. Then when I dye, the untreated part will not accept the dye. Here is a simple illustration: log cabin, dyed after weaving:

You could tie dye it if you wanted: