Change line color of .table-bordered in Twitter Bootstrap

Change line color of .table-bordered in Twitter Bootstrap

I am styling a number of tables with twitter bootstrap and am using the
.table.table-bordered class. The default border color is gray, which is
good for all my tables except one. For one table, I would like to change
this border color to black and also make the lines thicker if possible.
I've researched it and found the @tableBorder variable which I can
customize but changing this changes the color of all the tables.
I tried giving the table a class and putting this in the css file:
.differentTable {
@tableBorder: black;
}
...but that did not seem to change anything (not sure why).
Any help would be greatly appreciated.