The British rail trains do have yellow in their color schemes to show that it offers commuter services.

I believe it is so that the trains can be seen at night time (when it's dark) and many the Network Rail's stock are yellow. Network Rail manages all railways in the UK.

The extinct birds in India are Dodo, Emu, Labrador ducks, Quail, Red-billed Rail, Lysan rail

If leaking from the rail itself, the rail will need replaced. If leaking from a seal at the rail, replace the rail.

A Hogged Rail is the surface defect of the rail in which the rail ends are bent downword at the joints.