Most of the late 60s CB&Q Green was "BN Green", as the original idea was to add the "Northern" and BN herald after the merger. However, there was another, darker green, about which I have no information. This is probably the green used on BREX insulated boxcars, but I wouldn't swear to it. The difference isn't just weathering or a bad batch of paint.
I believe 15040 and 39997 are the result of dirt and weathering, and were originally BN green. As far as I know, all of the cars with the BN style name were BN green. Note that 47716 has the older lettering style, which seems to go with the darker green.