Well Howdie and Welcome!!
Double cast is kewl and fast. I think the easiest way to make stripes is to pick up the new yarn and beginning knitting with it. Some people tie on the new yarn. And that's fine too. The only reason I don't do is because of the knot it creates. Of course you could undo the knot when it's time to weave at the end
Also - remember that the edges will curl if you use only stockinette st. I recommend add 3-5 knit sts to creat a border so your edges won't curl. Of course, if you want the edges to curl, then stockinette away
Enjoy and do post updates on progress!!! We just love that ... :drool:
PS: 'tain't nothin' wrong with a 'lil acrylic :mrgreen: