Coloring the sideblocks and the column background uses the same principle e.g. assuming you use <td id="leftcolumn"> then this should work:

#leftcolumn {
    background-color: red;
}

But you can also be more specific and style things within these columns differently too e.g.:

#leftcolumn table  { border: thick solid red; }

#leftcolumn td  { border: thin dashed red; }

#middlecolumn table { border: thick solid green; }

#middlecolumn td { border: thin dashed green; }

#rightcolumn table { border: thick solid blue; }

#rightcolumn td { border: thin dashed blue; }

I think the relevant places to change in those file's I listed are relatively easy to find, though you may need a minimum familiarity with PHP.