[imported_ogden2k]

There needs to be some specific rules here, everything HAS TO BE XHTML compliant! That code is not!
This is how it should be:

<blockquote>
<table bgcolor="#000000" cellspacing="0">
<tr>
<td><font color="#FFFFFF" size="1">Spoiler:</font>
<br /><font color="black">{param}</font>
</td>
</tr>
</table>
</blockquote>

There's a better way to do it with CSS if you want(XHTML compliant too):
In BB custom codes, add a new custom code:

<font color="#000000"><strong>Spoiler</strong>:</font>
<br /><font class="spoiler">{param}</font>

Under style manger, Additional CSS Definitions, add:

.spoiler {
    color: #B7B7B7;
    background: #B7B7B7;
}