That's all true. Though the trouble I've had with monofilament is that it's "pokey" even after you've trimed and trimed and trimed all the little threads. The quilt I made this past summer has just now reached the point that it doesn't poke me when I mess with it, and I used it for the applique not even the quilting.
I think the end all be all key is do you want your quilting thread to be seen? If yes go with something that contasts, if not pick something to blend. :) In the case of the red, green, and yellow quilt you're working on any one of those colors would be good to use for quilting, and can look very pretty on the reverse as well.
I've found that buying a nice spool of one color for the quilt allows me to peice and quilt the entire thing, with a bit left over to use for other projects. In your case I seem to recall your sewing machine came with a whole bunch of thread, if it's cotton you can just pick whatever color matches that appeals to you.