The oil has turned black, does that mean I have to change it?

That the oil has a very black color isn't indicative of its bad state, but a sign that it is doing its job correctly. In the engine combustion process, soot and other impurities are generated that the lubricant must collect.

The cleaning of the internal organs of the engine is one of the lubricant’s functions, so it must necessarily darken with the passage of time.