what code would I put in my stylesheet to color the background of my tables?

Same as you would a BODY one.

Either in the tag itself...
style="background-color : #ff0000;"

Or in the head area...
table {background-color : #ff0000;}

Or as a class to be used in a specific table only...
.TableColor {background-color : #ff0000;}
...
class="TableColor"

And so on.