Message: hi! i have a king size comforter that i'd love to tie dye yellow and blue. i do not want it to be green at all and i wonder how to go about this. do i need to dye it yeoow then tie it and sqirt blue? or what? thanks for any help!

First, is the cover of the comforter 100% cotton? Synthetics cannot be dyed with the same dyes that work on cotton and silk.

Next point: all dye, of any type, is transparent, so any part of the comforter that gets both yellow and blue, whether at the same time or in different steps, WILL be green.

To avoid any hint of green, you can either make quite sure that yellow and blue go only on different parts of the comforter - this is quite difficult with tying - or you can use opaque fabric paint for the second color.

Fabric paint is not as nice as dye, because you can always feel the paint on the fabric. A high quality special fabric paint will change the feel of the fabric only a little, but lower quality fabric paints and acrylic paint can make the fabric quite rough. Unfortunately, there are few fabric paints that are truly opaque. Opacity is easier to obtain with a thick coating of fabric paint, but this has obvious effects on the feel of the fabric. Look for opaque fabric paints on the following pages:
http://www.dickblick.com/zz029/00/products.asp?param=0&ig_id=5237
http://www.fabricstodyefor.com/jacquard/jacquard_dyes_paints/neopaque.htm
http://www.prochemical.com/catalog/opaquetextile.htm

I recommend that you use only fiber reactive dye, such as Procion MX, when dyeing cotton, because its heat requirements are minimal and it is very bright, easy to use, and washfast (that is, it does not wash out). You could use blue dye and then add opaque yellow fabric paint, or you could use blue dye for tie-dyeing, complete that step with washing and drying, then carefully hand-apply yellow dye, on the places where the comforter stayed white in the blue-dyeing step. Note that the yellow dye tends to
spread more easily than other colors, so use just a bit until you see how far it is going to spread. Soda ash can be used as a pre-soak before dyeing, or added to the dye itself. The latter may be preferable for the yellow-dye step, since wet fabric encourages dye to spread farther. In the blue-dyeing step, be sure to tie very tightly with rubber bands or artificial sinew, so that enough areas stay white afterwards.

Dyeing a large, bulky item is much more difficult than dyeing something small, just because of the unwieldiness. I strongly recommend that you practice on t-shirts or inexpensive cotton pillowcases.