I would choose another solid color, either another green or a yellow. As you said use the different blocks in the center and at the corners. This will look like you planned the quilt this way.
Then use your green print as a narrow border.
This will frame the quilt top.
Then add a wider border in a great colorful print. :thumbup:

I haven't read all the replies yet, but how about this:

Make the border (with the print) wider than the mint borders, to go around your dark butterfly and then add a small strip of the print to go between all the mint borders. That would isolate and frame your dark butterfly as the center, but tie in all the mint-bordered light butterflies. That would work if your quilt is only the 9 blocks that you have pictured.

I think there have been some great suggestions here. Isn't it great getting input from so many? Each person sees things a little differently, so it gives you a lot of options, and usually one or two really sync with your tastes too.

Just wanted to say, that I think this is going to be one nice first project. You should be very proud of yourself.

I agree! I just love your butterflies!

I think the floral is too busy - suggest trying another pale pastel colour taken from your butterfly prints. You can arrange the different border print your wqay or alternate colours.

Good luck!!

The nine blocks shown were only a part of the quilt. I have 22 blocks of the mint green and 8 with the floral. I'm thinking one in each corner, one on each side of the black butterfly and one above it. I'm thinking of adding a 5 in. border on each side since it isn't wide enough for a king bed, but it is long enough. The blocks are 5 across and 6 down.

Nice butterfly blocks. It is ok to use something dif in fabrics--makes it more interesting.

I would stick with a solid around each block. In looking at the butterflies, which are beautiful, I keep seeing the soft orange tones in so many of them. I think I'd go with that color to frame the ones that are not going to be mint green. It's going to be lovely no matter which option you choose.
Hugs and smiles

Honestly, I think if you have something in mind and have heard all of the different opinions, you can do something that is suitable to your taste. I'd bet whatever you put together will be great. Be sure to let us see your final decision.

If you have some yellow, pink or blue if appropriate, use it and alternate it with the mint. I think the color should be different.