There are many taxis in Seoul. Many taxis with many different colours. However, please stay far away from the black coloured taxi. Even if it was the only taxi around, do not take it.
Why not you ask? Because the black taxi, also known as the executive taxi, is THE most expensive taxi in Seoul. This taxi has GPS, a driver that can speak more than 10 languages, credit card services and can drive you wherever you wish to go – for a price.
Typically used by business men and employees on paid business trips, it is NOT the taxi to use for those who are on holiday ( unless you are Bill Gates ). My travel agent told me about one Malaysian tourist who was in Seoul and desperately needed a taxi. Finding no other taxis but the black one, she got on and asked the driver to bring her back to her hotel not too far away.
Much to her shock, when she asked how much the driver told her 181522 won. I asked my Korean tour guide about the black taxi and he said yes they are really expensive but he was not sure what the current rates are at the moment.
Conclusion – do not take the black taxi unless you want to cut your holiday short.