They change colour and become darker if you do not wash them before the first use. It is due to the fact that during a production process, they are covered with a special protection fluid, which you need to wash off before the first use.
58 How can I find out whether or not the pan with a normal bottom is heated up, without placing a lid on it?
You should perform the test of a water drop. Pour a few drops of water onto the pan, and if the water starts to jump around, it means that the pan is heated up and ready to fry on.