From my experience, trying to match fabric online can be quite tricky.
What you see on your screen can be very different from the actual color.
Sometimes it's close sometimes it can be very different.

What a fabulous panel. How about a marbelled effect pluey grey to match the blue in the panel?

Try Thousands of Bolts. Beautiful panel

Hi aully,
Have you ever visited the Canadian site: sew-sisters.com ?
They are in Toronto, use PayPal and have some Stonehenge fabrics that might work well with your beautiful panel.