[R] plotting many unique colors with categorical data

[SavageMaDaMe]

Hi- I am trying to plot a matrix of categorical values across time using
color to represent each individual factor. For example:

   1982 1983 1984 1985 1986 1987 
1    19   19   68   68   19   19   68   
2    68   68   19   19   68   68   19 
3    26   26   34   34   26   26   26  
4    57   34   57   57   34   57   34   
5    34   57   26   26   57   34   57   
6    28   28   28   28   28   58   58 
7    60   10   58   58   58   28   28  
8    58   58   42   27   10   39   39 
9    22   39   22   42   42   27   42 
10   39   22   10   39   39   20   10 


 I have 75 factors which could be in different positions through out time
(26 years).  I've successfully created a plot using both ggplot() and
color2D.matplot(), but can not select enough distinct colors from the
default color palettes available to be able to view differences in the data. 
I've tried messing with RGB values, Brewer palettes, etc.  

How can I select colors from a list of available colors without choosing
ones which are too close in similarity to each other. For instance, I could
have several very similar blues, but if the Hue or saturation was different
on each, it would be fairly easy to tell the difference?  

Maybe there are too many factors to make this visual representation
effective?

Thanks in advance for your help!

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