Alison,
I think you can use a medium green on the front and it will disappear into the quilt top because the material is so busy. I've done that successfully on a bunch of the quilts I have made. Surprisingly, using a contrasting color on the top will not pop as much as you think, should you choose to do that.
Your best option? Test drive your colors on a scrap. Do the pink on the top and the busy green on the back. Change the threads till you get the effect you are looking for. This will also have the advantage of getting your hands going on the FMQ for the quilt.
One note: Most folks on the board and those folks who have been teachers of mine do NOT recommend using clear or smoky monofilament for the bobbin...too many tension issues since it stretches under tension.
Good luck!