Have a look at the Splunk Dashboard example app: https://splunkbase.splunk.com/app/1603
There are great examples that show you this exact usage under "Table Elements"
Example xml:
<panel>
<table>
<search>
<query>
index=_internal | stats count by sourcetype
</query>
<earliest>-15m</earliest>
<latest>now</latest>
</search>
<format type="color" field="sourcetype">
<colorPalette type="map">{"splunkd":#F7BC38,"scheduler":#6A5C9E}</colorPalette>
</format>
<format type="color" field="count">
<colorPalette type="list">[#65A637,#6DB7C6,#F7BC38,#F58F39,#D93F3C]</colorPalette>
<scale type="threshold">0,30,70,100</scale>
</format>
</table>
<html>
<ul>
<li>"sourcetype" column is using custom defined colors based on individual cell values.</li>
<li>"count" column is using custom defined colors based on cell value ranges.</li>
</ul>
</html>
