The plug for my laptop is slowly changing colour, is it still safe to use until I get a new one?
Marks like that suggest that one of the receptacles that you are plugging into may be worn out. they do not suggest a problem with your laptop power supply.

The marks on your plug are cosmetic only, they will not significanly affect its performance.

However the socket end of that extension cord is faulty and there's a potential for fire if you continue using it.