/* 1.1 Default background colour and text colour */
body {background-color: #fff}
.pun {color: #333}
div.box, .pun blockquote, div.codebox, #adminconsole fieldset th {background-color: #f1f1f1}
#adminconsole td, #adminconsole th {border-color: #f1f1f1}
Everything gets that colour unless the stylesheet says otherwise. It is set on div.box.
Does this make it clearer
/****************************************************************/
/* 1. BACKGROUND AND TEXT COLOURS */
/****************************************************************/
/* 1.1 Default background colour and text colour */
body {background-color: #fff} /*screen background*/
.pun {color: #333} /* all normal text */
/* 1.2 Background of main board elements - pale grey by default */
div.box {background-color: #f1f1f1} /* everything unless otherwise specified */
.pun blockquote, div.codebox {background-color: #f1f1f1} /* code and quote boxes in posts */
/* 1. 2 Darker background colour - medium grey */
td.tc2, td.tc3, td.tcmod {background-color: #dedfdf} /* darker columns in tables */
#postpreview {background-color: #dedfdf} /* post preview */
#viewprofile dd {background-color: #dedfdf} /* right hand part of information about other users in profile */
div.forminfo {background-color: #dedfdf} /* the information box at the top of some forms e.g. registration */
div.blockmenu div.box {background-color: #dedfdf} /* the vertical menu in profile and admin */
/* 1.3 Main headers and navigation bar background and text colour - bright blue */
.pun h2 {background-color: #0066b9; color: #fff} /* header rows */
#brdmenu {background-color: #0066b9; color: #fff} /* main navigation menu */
/* 1.4 Table header rows i.e. the slightly darker row for column headings */
.pun th {background-color: #d1d1d1}
/* 1.5 Fieldset legend text colour */
.pun legend {color: #005cb1}
/* 1.6 Highlighted text for various items */
.pun div.blockmenu li.isactive a {color: #333} /* link colour for verticial menus showing active page */
#posterror li strong {color: #333} /* text colour for error messages generated by invalid posts */
/* 1.7 Admin console colours */
#adminconsole fieldset th, #adminconsole td, #adminconsole th {border-color: #f1f1f1} /* pale grey background */
#adminconsole fieldset td, #adstats dd {background-color: #dedfdf}
/****************************************************************/
/* 2. POST BACKGROUNDS AND TEXT */
/****************************************************************/
/* 2.1 The darker colour for the right hand part of posts. */
div.blockpost div.box, div.postright, div.postfootright {background-color: #dedfdf}
/*2.2 The lighter colour for the left hand part of posts - both colour values must be the same */
div.postright, div.postfootright {border-left-color: #f1f1f1}
div.postleft, div.postfootleft, div.blockpost label {background-color: #f1f1f1}
/* 2.3 Background for post headers - the blue top part of posts */
div.blockpost h2 {background-color: #006fc9}
/* 2.4 the text colour for post numbers */
div.blockpost h2 span.conr {color: #aabdcd}
/* 2.5 This is the line above the signature in posts. Colour and background should be the same */
.pun hr {background-color: #333; color: #333}
