For having alternating colors for your threads add the following code at the top of the threadbit template.
Code:
<vb:if condition="$altrow =& $GLOBALS['altrow']"></vb:if>
<vb:if condition="!isset($altrow)">
    <vb:if condition="$altrow = 0"></vb:if>
</vb:if>
<vb:if condition="++$altrow % 2 == 0">
    <vb:if condition="$rowClass = 'alteven'"></vb:if>
<vb:else />
    <vb:if condition="$rowClass = 'altodd'"></vb:if>
</vb:if>
And then edit the first line of the code as follows.
Change
Code:
<li class="threadbit {vb:raw thread.statusstring}
to
Code:
<li class="threadbit {vb:raw $rowClass} {vb:raw thread.statusstring}
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