do a 3.5 or a 4.5 inch border mamahen.
I think your patterned fabric is not too bold to bring out. Medallion quilts are busy. Face it. lol hard not to be with so much going on. The trick is to accent the center. I think more of the green would be great. If you want you could continue to use it as a slim line between rows or every other row.. a focal accent. Or you could chose to add it in the row itself. I would advise you me big queen of advice lol to make a couple blocks of whatever colors your thinking off using.. stand back and give it a look, squinting at it. does it make you happy? does one color stand out way too much for the others or does it compliment the quilt as a whole? I learned the hard way to make a couple blocks first before I cut enough for an entire round. You will find your much happier if you do this trust me unless your super great with colors and values. Even then sometimes it just doesn't work so check it out before you cut a whole bunch!!!