The correct answer is green.
A point indicator is a light that is used to indicate the position of the points on a railway track. The points are the movable parts of the track that allow trains to change direction. The point indicator is usually located at the entrance to a siding or branch line.
If the points are set for the main line, the point indicator will show a green light. This indicates that the track is clear and that trains can proceed. If the points are set for a siding or branch line, the point indicator will show a red light. This indicates that the track is not clear and that trains should not proceed.
The other options are incorrect because they do not represent the correct color of the point indicator when the points are set for the main line.