if you layer the strands and colors evenly, as shown in my vid, it works just fine every time.
i'll add the following ...
one thing that i consider a quality about endless strings is that they don't need a lot of twists. just enuf to round off is all that's required.
if you use two or more colored strands, the results will look like the pix above, with not much twisting. this doesn't have that serious twisted look of a flemish bowstring.
so, adding about 1/4" to the length of yer string will allow lots of added twists to simulate a flemish bowstring's barber shop pole, candy cane look.