Here are a few maps to show my recent Japanese castle changes, these are also good examples of what all the colours mean in "diff" mode
Before: (Tokyo Unified Nagisa'10280231'55)
After: (Tokyo Unified Abarai'79417283'56)
Red means blocks got removed (change into "air")
Green means blocks got added
Blue means blocks got changed (different type of block or different colour)
If two things happened in the same place on the map the colours get combined.
some red areas on the left edge are where I removed blocks (with TNT) and left bare dirt showing.
purple/magenta are where I excavated with TNT and then either covered the bare dirt with grass or filled it in with water.
there is a lot of green next to the purple. that's where I built the wall right on top of the existing ground without digging first.
the light blue (cyan) areas are where I added layers of dirt to build it up, but I always change grass to stone or dirt first because I don't like to put grass on top of grass (even though you usually can't see it, it still bothers me somehow)
there's also light blue in a water area near the top. I had to raise that water up one block so the whole moat would be at the same level. I also made the water a darker shade of blue. so I added blocks and changed blocks: green+blue = cyan
in the mostly white areas (rectangles) I changed everything. That's mainly the three buildings I rebuilt.
a couple small yellow blobs are trees that I either raised or lowered: add leaves to the top, remove leaves from the bottom. red+green=yellow
near the top-centre is a blob that is red and green. That's a tree that I moved sideways.
a bunch of trees have red dots in the corners. I don't like the 5x5 square trees so I remove the leaves from the corners to make it look more round.
near the middle is a mostly blue rectangle (a big building that had a moat around it, I changed the water to dirt). Inside that building is a curious shape that its symmetrical, with a green top half and a red bottom half. I moved the front door of that building to the opposite side and I had to move a lot of the inside of the first floor to match.