Gleditsia seed pod

The large, flat seed pods of the Gleditsia in the garden are maturing, and look slightly out of place among the tree's tiny golden leaves and fine lacy fronds. But away from the foliage, they look very attractive in their own right as they turn from bright yellowy-green to a deep uniform brown.
The pods don't seem to go for the more common maturing process of graduated colour changes starting from fully green and progressively darkening to their final all-over brown.  
They prefer to change colour along a very defined dividing line running along the length of the pod, and curving tightly around the edges of the seeds underneath. On either side of the line, the pod is either fully green or fully brown, with no graduated shades in between.
While the end product is still a large brown pod not dissimilar to those of hundreds - possibly thousands - of other tree species, the process of getting there is just a little bit more interesting, and appealing.
This tree is a specific variety of Gleditsia developed for use in suburban gardens - triachanthos var. inermis, I'm told. Fear not, it is not a Gleditsia triacanthos (period), or Honey Locust. 
These are renowned for their truly vicious thorns that can puncture car tyres and injure livestock, and their rather ungenteel habit of hyper-invasiveness that's the scourge of broad-acre farming in many regions, especially Australia and North America. They are highly adaptable to a very wide range of soil and climatic conditions, so it's not really surprising that they've earned notoriety as a major invasive environmental and economic weed.
So suburbanised Gleditsias of the inermis variety are always keen to distance themselves from their more disreputable, unrefined and prickly country cousins.