Its about time that you should change the oil filter and oil.
By the way, which engine oil r u using. The engine oil is supposed to do 2 things, lubricate and clean the engine.
A light colored engine oil after 5000km could also mean it didnt do a good job in cleaning the engine and getting rid of the sludge that gets build up in the engine from the burning gasoline.
is ur car running on CNG? thats supposedly burns cleaner than petrol. so it could be because of that. otherwise use better engine oil.