This is like the ball shaped one that Workbench posted, but only one block.
it has a dark center much like you described...so ....maybe??
jenny doan at MSQ did a tutorial years ago...
https://saidwithlove.com.au/curved-log-cabin-tutorial/
pinterest has more here (scroll down)
https://www.pinterest.com/pin/178103360266654205/
It might help to search for 'offset log cabin block'