These just became available and "each color CD contains a unique secret bonus demo track".
Links to Paul's US store:
https://shop.paulmccartney.com/collections/mccartney-iii-white-box-sets
https://shop.paulmccartney.com/collections/mccartney-iii-red-box-sets
https://shop.paulmccartney.com/collections/mccartney-iii-blue-box-sets
https://shop.paulmccartney.com/collections/mccartney-iii-yellow-box-sets
Links to Paul's UK store:
https://shopuk.paulmccartney.com/*/McCartney-III-White/
https://shopuk.paulmccartney.com/*/McCartney-III-Red/