Why cabs has got different colours in other towns?

We can see that there is a lot of variety concerned of colours of cabs in our world, f.ex in New York we can find just yellow cabs, there is no possibility to find them somewhere else. In UK is the same, in London are only black ones, in special models. Special cabs we can see in Barcelona- black & yellow taxi etc. There are many examples of this event.

Why is it like this?

I think, that the answer isn't difficult. To understand it properly, we can compare cabs to the architecture, traditional food & clothes etc. Cabs just are something which character our capital/country. If we will think about New York, probably the first picture in our mind , likelihood we will see the yellow cabs, does it strange?