column's height with background color

Hello gurus
I am working with plone 2.0, and i am trying to get the full control of
columns in main template. 
 
I would like to manage  the color of the background in the left column
(or column one), trying to fill all this column with  the same color.
But also if I set "height 100%" he just fills the space right to contain
the contents in the column itself. The only I have found till here is
just to set height as exact value (but this may lead to other problems).
 
I am not an expert of css, but what I know is that columns are not
managed with tables (as in plone 1.0) but with "float" instructions in
css...
 
Someone has experienced the same problem?
 
Thanks!
Claudio