I have this in a fbClassOptions script:
<script type="text/javascript">fbClassOptions = {myPop:"boxRoundCorners:'all' boxColor:#800000|#121212 outerBorderColor:#22a8f5 innerBorderColor:#2090ff textColor:#203870 strongTextColor:#800000 boxCornerRadius:50 contentCornerRadius:36",};</script>
If I drop the second boxColor and use boxColor:#121212 it works fine. The radius is intentionally exaggerated for this example.