It's a two step process:
1) open events_css.css in the compontents/com_events directory and find the .cal_table definition at the top. add:
to the definition, where "red" is the color you desire.
2) open events.css in the same directory. go to line 2031 and change 'cellspacing="1"' to the width you want.
save both files and refresh the page.