Add changelog for dashboard theme presets

src/changelog/2026/08/dashboard-theme-presets.md

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+---
+title: Theme Presets for Dashboard
+description: Start a Dashboard theme from a built-in preset — Light, Dark, Dracula, Nord, or Sepia — instead of picking colours by hand.
+date: 2026-08-14 12:00:00
+authors: ["noley-holland"]
+tags:
+  - changelog
+issues:
+  - https://github.com/FlowFuse/node-red-dashboard/issues/454
+  - https://github.com/FlowFuse/node-red-dashboard/issues/1538
+---
+
+You can now start a Dashboard theme from a built-in preset — **Light**, **Dark**, **Dracula**, **Nord**, or **Sepia** — and get a complete colour scheme in one step, instead of setting each colour yourself.
+
+Every preset meets WCAG AA contrast, so your dashboard is readable on the first render. No checking dark-scheme text against its background before you ship. And nothing is locked: change any individual colour and the theme flips to **Custom**, keeping the rest of the scheme intact. New dashboards start on Light.
+
+Dark themes adapt automatically. When a theme's page background is dark, Dashboard switches input fields, borders, chart and gauge colours, and the browser's native date and time pickers to match, so nothing sits light against a dark background. This applies to any dark theme you build, not just the presets.
+
+To get started:
+
+1. In the Dashboard sidebar, click **+ Theme**. The new theme starts from your default preset.
+2. Open it and use the **Preset** dropdown to switch schemes.
+3. To change which preset new themes start from, set the **Theme preset** dropdown in the sidebar.
+
+![Adding a Dashboard theme, switching its preset in the editor, and previewing Light, Dark, Dracula, Nord, and Sepia](./images/dashboard-theme-presets.gif)
+*Switching presets updates every colour at once — the same dashboard, five schemes, no per-colour editing.*
+
+This feature is available to all FlowFuse Dashboard users on FlowFuse Cloud and Self Hosted, from Dashboard v1.30.3.