Huh. The strings will have eaten slightly into the top edges of the holes in the tie part of the bridge. You should have the same effect on the holes and the edge of the bottom part of the bridge. After a while, the strings tend to wear a groove into the wood. I suspect that the lighter wood is a bridge repair or Kamaka's early attempt to mitigate this wear. Later they inset strips of bone or plastic to do this and created the signature look on their ukes. If the edge has little to no wear, then it is newer than the rest of the bridge.
The saddle looks like it has had a homemade modification. The top has been filed down. Creating a squared top which I don't think is good for the sound. You want a single point of contact between the saddle and each string. A squared top creates two. The slant is a compensation for the strings, but I can't help to wonder if it's accurate? It looks pretty close to the compensation in the 6 string photo.
You might want to check the nut for similar adjustment.
From what you have shown, it looks pretty nice.