Well, actually 50 is kind of a bad answer. They are saying that the upper bound is related to the number of regions (i.e. the coloring is trivial). There is nothing particulary good in that. They only recognize that they need as many colors as the number of regions. What if there are 800 regions? How can they find 800 different colors? Let me tell you this little "joke".
Umberto Eco, an Italian semiotician and essayst (not certainly a mathematician!) once proposed the "Theorem of the 800 colors": 800 colors are sufficient to color any map. There are two main problems. First you have to find a map with 800 regions, second you have to be able to describe (hence distinguish between!) 800 colors. This is more a joke, but it's relevant (I don't really know where you can find this, but I guess there is only the Italian version, somewhere)