LA quilter here. Don’t quilt it too densely. Match to the light lime green on the front. Although grey often is great for blending in, I think it could would take away from the vibrancy of the colors on the front which are beautiful. Do you have any fabric left you can try it on? If not don’ t just hold the spool up to the placemat. The layers of thread on the spool intensify the color. Pull some off the spool and puddle it on the fabric. Move the puddle around to different areas to see how it will affect it. Also don’t make your quilting stitches too long. Longer stitches make the quilting more visible. All of this, of course, is offered as “in my humble opinion”.

I agree with everything FWLover said, and want to add to use a fine thread. Bottom Line is a 60 wt thread, Microquilter is a 100 wt thread, I would use something in this neighborhood.

For something like this I might try a variegated thread.

I agree with quilting shorttimer - pale green.

Pale green gets my vote.

Colors that blend very well are a v-e-r-y pale yellow and/or peach. They blend in most fabrics. You will be able to see the quilting from the back because that fabric is solid. I would quilt this a little dense to make sure it is flat so when you place glasses etc on it they will not tip over. Don’t have to quilt it to death. Hope to see what you do when you post later.

Thank you so much .....I will take the advice, buy a lighter weight, pale thread, try it on a sample piece and see what happens.