How do you do 3 color in double knitting?

i’m trying to knit a scarf with black and red, but i want to add new color so the scarf have 3 color, (2 on each side) how do i do it?

Well, I think you’d just need 2 strands of your third color, and you could just carry that along and use it when necessary… That might get complicated though (and I can’t think of how to describe to do it) :shrug:

but wouldn’t there be a loose end? how do i tight the end up?

As it’s a (tubular) scarf you can just tie the ends of the third colour inside to secure.