I don't know the purpose or reason for the border, but I would just add the style directly (or use a class).
I also feel I should mention that adding a border to 1 cell actually affects the spacing of other cells (as borders increase the outer size of an element). You could alternatively use the 'outline' property instead of 'border' if you wanted to give a border effect without altering the spacing/size of anything in the table.
<td style="border: 1px solid #5B5;">B2</td> <!-- Only this cell should have a border -->
"Given billions of tries, could a spilled bottle of ink ever fall into the words of Shakespeare?"