I like the colors - but it sure does look a challenge for several reasons:

The fabrics and colors chosen - I think it will be "something" to find colors that will "go" with it
The design made
The measurements of it - as mentioned - 25 and 14 have no common factors in them

I think keep to the purple and green but add black and white accents. I would add another color if there was a fabric that had the purple and green with an accent.

There is a great Craftsy class on borders by Winnie Fleming. This link is Pat Sloan reviewing the class http://blog.patsloan.com/2014/10/pat...l-borders.html

The pictures in the review might give you some ideas also. The final picture is a border print added with a miter. You might consider adding a border that will give even number of inches per side to the next person in the swap.

I was thinking flying geese in opposite corners with a different fabric that has either the purple or green with a black, white or grey. Or go with same color combo of either color and the black, grey or white and checkered corners

Omgoodness........I'm glad it isn't me doing this one. Can't wait to see what you come up with.

I have no suggestions, but WOW...I love the color combo and design! Look forward to seeing what you decide.

There was a free Craftsy class in 2014 Block of the Month Color Theory. Lots of bold contrasting colours were used in the class.

I do not know if it is still free to access, but you may get some ideas there.

I love the purple/lime colour combination. I know nothing at all about round robins and the rules for them, but are you allowed to cut down the block? If you can trim it to 14X21, both sides will be divisible by 7. Or 12X24 would give more options, divisible evenly by 2, 3, 4, 6.

I too would choose orange or an orange-red and cut down the center to be divisible evenly in both directions.

What about a border of tumbler blocks, in purple, green, orange and cream?

This makes me think of a frog fabric I have. So I'd get a green frog paper piecing pattern. Put a frog near each corner, surround each frog in a light, and then do the rest of the border in a purple print that includes green.

Or do a tonal green border and applique giant purple polka dots on it :-). The appliqued fabric should have a few other colors in it, like a purple background with bright rainbow dots. Or frogs. Let it be something with frogs!

This lends itself to whimsy. Don't do anything serious.

I would choose another colour as the lime green is a difficult colour to match .unusual sized centre is it the correct sizes.?my school colours were purple and dark green.