You can create your own custom color palletes. I'm not sure what the limit on the number of colors is. However, I don't think it's less than 52. You can find more information at
Let me know if this helps,
You might find this helpful: http://tableaufriction.blogspot.com/2012/11/finally-you-can-use-tableau-data-colors.html
it contains an enumeration of all of the colors Tableau uses in its palettes, at least in v7.