I have a second story addition that was just added on. With how the upstairs sits, I want to visually separate it from the lower floor and am going to use a different color.
Two of the four exterior walls have a natural break that will be no problem, but the other two walls are two story flat walls.

The question is, what is the best way to join the two colors of siding? My plan was to use a trim board at the joint and stain/paint it the color of my trim pieces (brown). However, I am uncertain of what goes on behind this trim board to ensure the seam will not allow water penetration.

If I join the two types of siding, how does the trim pieces sit over this w/o puncturing the siding?
If I leave a gap, how do I flash to properly be sure that water sheds correctly?

Thanks for any help!