Perhaps even a [tr=#XXXXXX] if we want to set the same border color for the whole row in one code.
Alternatively, since text inside the cells do not inherit external formatting, color codes around the [table], [tr] and [td] tags could also color the table and cell borders.
EDIT: I've just noticed though, that when replying (not quick reply) below the text box where you can review the lates n posts (afaik 10) table boundaries aren't displayed and text is like just floating there.