Hi Frank,
Do you want display "Cells" in alternate colors or "Rows" in alternate colors.
If you want to display "Cells"
i don't think you need some help 'cas you might be writing all "Cells"(<TD></TD>) you can simply specify the color.
If you want to display "Rows" then
in your while loop(in getting data use this)
$row_count++;
if($row_count%2==0){$color="grey";}
else{$color="green";}
Now set the BGCOLOR attribute of table cell to $color i.e <TD BGCOLOR=\"$color\">