never seen or heard of this technique earlier...

For emergencies such as fractures detected in track, a spare joggle fish plate and clamps are tied to the track at, say, every km. These are colored for easy identification of the JFP as a spare and not protecting a defective weld.

The fire and smoke you see here is caused by a hot axle. Station staff, gatemen and the like are expected to be vigilant and report such matters (observed on passing trains) at the earliest possible.

Finally! a fellow IRFCAn with a Canon A410! I thought I was the only one stuck with it... Canon Rulz man! I think this colour accent/colour swap is a new addition in Canon.

No Ashwanth, not all digital cameras have this feature. In fact, this is the first camera where I am hearing of this feature.

No photoshop.No playing with layers.This image went straight into the gallery after resizing.My camera(canon A410) has a "colour accent" feature in the manual mode.Here i can select any one colour from the scene and the camera will retain that colour alone in the scene.For example if there was a woman in red saree near the signal,her saree too would have retained the colour.In this case,I picked the colour from Naveen's red coloured shoulder bag.Similarly in another mode,I can request my camera to change colour A to colour B.Am sure all digital cameras have this feature.

Its very simple...take any image editing program that deals in layers. Create duplicate layer of the photo, change one of the layers to BW, erase BW layer at the object you want to retain in colour. Merge layers, flatten image. You are done. More examples here - flickr.com/photos/gvarshney
GIMP is open source (and free) equivalent of photoshop.

Could you kindly share how you could shoot the whole image in BW and get the signal in color?