it looks like someone painted them without a plan
That's the BN way.
Seriously.
There truly is no such thing as BN Green. Many shops painted locomotives, and there was no consistency in precisely what color they were painted. Even at the same shop, there was no particular consistency. I worked at Havelock Shops for a number of years, where many BN locos were painted, and asked the guys in the paint shop (at one time, I was looking at modeling BN, and painted a number of units) and they said the color was different all the time. Sometimes dark, sometimes bright -- as long as it was Green, it was good.
Sometimes in modeling the differences can be starker than one would like. A little light weathering will usually smooth out the majority of the variation and bring everything down to something a little more consistent.
