Extra shades is not a standard feature of the diagram, in the sense that it cannot be specified by a parameter in the Diagram definition, like startShade=.... can specify an alternative darkShade for making the diagram look nicer when it hasn't been used yet. The script does have an internal variable, though, that you can set by adding extra JavaScript on the page, like
<script>oddShade = "#E04040";</script>
This would define an alternative startShade for the dark squares with odd coordinates.
There is no provision for an alternative lightShade.
Extra shades is not a standard feature of the diagram, in the sense that it cannot be specified by a parameter in the Diagram definition, like startShade=.... can specify an alternative darkShade for making the diagram look nicer when it hasn't been used yet. The script does have an internal variable, though, that you can set by adding extra JavaScript on the page, like
<script>oddShade = "#E04040";</script>This would define an alternative startShade for the dark squares with odd coordinates.
There is no provision for an alternative lightShade.