Tried but it dd not help :-(
For your info - my mail.css file now reads as following:
<blockquote class="quote light-black dark-border-color"><div class="quote light-border-color">
<div class="quote-message">
<i>#content, #mimemail-body {
  background-color: white;
}
body  {
	background:#fff;
}</i>
</div>
</div></blockquote>


<quote author="KOBA | Hans Rossel-2">
Did you try
Body {background:#fff;}

Hans

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