That's hard and I understand your dilemma. Often the same color trim is used to unify rooms that are different colors. But if you are painting the rooms in different shades of the same color family, that might not be needed because the room colors will already be unified.

What about just painting the kitchen frame trim green, but not the passageway frame to the other rooms and the trim in the other rooms? Maybe you could go with a soft white like SW Dover White (looks nice with green) for that.

Don't be concerned about splitting the colors. I did that between rooms I had with stained woodwork and ones where the woodwork was painted. Until I finally painted over the stained last year. You just have to find the right spot to split to colors, even if you have to do a sample and see how it looks.

It's common for different rooms to be different colors. I follow one rule of thumb. Colors follow formal traffic flow. Flooring materials and thresholds often follow this same rule of thumb. Color and materials should *spill* from the front of the house (the path you would follow walking from the front door into each of these spaces) to the less formal back of the house.

Color harmonies from one room to the next usually take care of themselves. It often happens naturally. Odds are you would not choose a color for the dining room, for example, if you did like how it looked juxtaposed to the living room -- so naturally any juncture where the two colors meet will look just fine.

I've colored against this rule of thumb before. I call it coloring upstream lol! :D and I haven't been able to make it work. It looked off to me and those involved and I ended up having those areas repainted to follow the staid *color spills to the back* rule of thumb.

Not sure if this is the kind of color transition you were talking about or not, but hope it helped some. :D