This could be done as follows:
code for categories.tpl:
This will then say for each category item it will look for a style in the style sheet of CategoriesList123 or whatever the category id is.
Then simply create a style sheet class for each category id as follows:
.CategoriesList1{
FONT-SIZE: 12px;
COLOR: #330000;
}
.CategoriesList2{
FONT-SIZE: 12px;
COLOR: #FF9900;
}
.CategoriesList3{
FONT-SIZE: 12px;
COLOR: #FF3300;
}
etc etc etc .............
hth