If something looks like real metal in your Happy Bungalow, then it is.  The metal can rust or oxidize (change color) over time.  This will be much more pronounced in humid environments.  Kept in conditioned spaces, you should have no troubles.

If the finish dulls: 1. sand lightly with extra fine grit (600 or above) sandpaper, 2. scrape off with the edge of a sharp knife (X-Acto or similar).

Note that the magnets in the robots should not be sanded or scraped – they are too fragile for this.  Also, they are chrome plated, so they should not discolor.