v9: How do you specify light and dark colour schemes in atlassian-plugin.xml?

[Calum]

We've been using Confluence Data Centre v8, and have a custom plugin that specifies its own colour scheme. In our atlassian-plugin.xml, that looked like:

<colour-scheme key="our-color-scheme" name="Our Colour Scheme" class="com.atlassian.confluence.themes.BaseColourScheme">
  <colour key="property.style.topbarcolour" value="#312D2A"/>
  <colour key="property.style.breadcrumbstextcolour" value="#FFFFFF"/>
  <colour key="property.style.headerbuttonbasebgcolour" value="#C74634"/>
  .
  .
  .
</colour-scheme>

Now we're about to upgrade to v9, and this no longer works—our colour scheme is not applied, and does not appear in the space Look & Feel panel as an option to apply. Also, we can find no documentation on how to specify a similar colour scheme for dark mode, which we now have for the first time.

What should we be doing here?