Region Maps at the moment don't do much. It's used for the depths addon. The the Collision Map demo, I used to have an event where it could only walk on that colored area in the region map, but I forgot to add it back in.
If you want to make an event that can only move on a color in that region map, you would first need the Region Lock addon and add this in the event:
<region=#0000ff>
That's assuming the color I want them to be able to move on, on the region map, is blue. There are more examples of that inside the Help for Region Lock addon.
You can also grab the color at a position using the script call, which can be used for making some "advanced" stuff
$gameMap.getPixelRegion(x, y);
x and y are in pixel values.
If you just use "$gameMap.getPixelRegion();" That will return the color at the players location.