Ok, we told you how to change the background before and you said that's not what you was talking about and I thought you was talking about the outside not where you type on the WYSIWYG editor.
As we told you before the background is held on strIETextBoxColour on the skin_file.asp, if you got it set to #444444 and it's still white then there's something wrong with your forum. The text color is Text on the css file.
Alternatively you could open IE_textbox.asp and change line 210 from:
<body bgcolor="<% = strIETextBoxColour %>" class="text" leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">
to:
<body bgcolor="Bacground Color Here" Text="Text Color Here" leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">