In a custom dashboard, I was able to get JSON to display with syntax highlighting by setting maxLines to 0. (All Lines)
<event>
<title></title>
<search>
<query>*</query>
<earliest>0</earliest>
<latest></latest>
</search>
<option name="list.drilldown">full</option>
<option name="list.wrap">1</option>
<option name="maxLines">0</option>
<option name="raw.drilldown">full</option>
<option name="rowNumbers">0</option>
<option name="table.drilldown">all</option>
<option name="table.wrap">1</option>
<option name="type">list</option>
<option name="count">10</option>
<fields>["host","source","sourcetype"]</fields>
</event>
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