So, I went ahead and knit it with the yellow. The good thing is that I love the yellow color. It's a very beautiful color and it fits well with the dark-brown. The bad thing is that it's way to bright compared to the green, and much brighter than the pictures on the internet indicated (manufacturer and store). So the two colors are in two different tones and the yellow stands out too much. Oh, well. I do really like the dark-brown, moss-green, yellow combo.
I'm knitting the collar and is almost done. I have to finish the sweater before we move (in 2 weeks), both because I need a sewing machine and because I need to wear it in Ohio. I