It has been my experience that a gold colored thread goes with just about everything. So does a sage green.
Another option you can consider is a very fine thread like invisifil from Wonderfil threads. It is a 90 wt polyester that sinks down into the fabric and reflects whatever color fabric it is sitting on. On the below quilt I used Invisifil in the sky which was many different shades of fabric. You don't see the thread at all, just the texture left behind by the quilting. I think I used a light sky blue color but can't remember for sure.
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