There's an easier way to do this without modifying your header or templates... and will do the actual posts as well as the index page.
Just go to Styles --> Modify --> fonts/colors/etc --> Main Colors
Add the code to your First and Second Alternating Table Background Color replacement.
My code reads this:
First Alternating Table Background Color:
#545454" style="BORDER-RIGHT: #303030 2px solid; BORDER-TOP: #c0c0c0 2px solid; BORDER-LEFT: #c0c0c0 2px solid; BORDER-BOTTOM: #303030 2px solid;"
Second Alternating Table Background Color:
#646464" style="BORDER-RIGHT: #303030 2px solid; BORDER-TOP: #c0c0c0 2px solid; BORDER-LEFT: #c0c0c0 2px solid; BORDER-BOTTOM: #303030 2px solid;"
The result is
This
You can copy and paste this in yours, then just replace the hex code with your colours, and adjust the px value if you like.