Sounds like what you mean. Light greenish tint with a purple ‘eye’ where they attach to the pod when at the shelling stage. Turn white, with increasing purple swirls as the mature; then at full dry maturity, a dark purple. with white flecking. Seeds about the size of baby limas.
From what I’ve been able to find on the Net to look for might be “Dixie” butterbean or Jackson Wonder Butterbean. Both of these look a lot like, but not identical, to what I have.
Justadumbblonde sent me the seeds 2 or 3 years ago.