since this took me longer than a monkey on a typewrite to work out, I thought I would post this. I wanted to have a different color background for posts (green) and pages (white). (don't ask why).

Setting every page and post backgroud green is in Style and Edit Center Column/Center column Style, then add background: green;

this seems to work (atahualpa 3.5.3, because my ISP doesn't run current versions of php.)

this bit of php goes in ATO/add HTML/CSS inserts/CSS inserts.

<?php if (is_page()) {?> td#middle {background: white} <?php }
?>

i.e, <?php turn on php, run if () statement, with wordpress is_page() function, then if true {execute a block of code, ?> turn off php, and set CSS style for td#middle {background: white} turn on php, finish block of code } (which doesn't have a semi-colon after it) and turn off php ?>

I discovered it was td#middle by changing the colours, and looking for what changed in the view source, in the <style="text/css"> section, which needed configure CSS &JS/CSS to be set to inline.

I suspect there are better ways of achieving this.

You perhaps could use the following in ATO>Add HTML/CSS Inserts>CSS Inserts

.type-page {
background: #fff !important;
{
.type-post {
background: #greenhexcode !important;
}

Aha, I would guess an even better soln. appreciated.