diff --git a/README.md b/README.md
index ed7dddb..a26befd 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,6 @@
 [![npm](https://img.shields.io/npm/v/nextline-web)](https://www.npmjs.com/package/nextline-web)
 [![Unit tests](https://github.com/simonsobs/nextline-web/actions/workflows/unit-test.yml/badge.svg)](https://github.com/simonsobs/nextline-web/actions/workflows/unit-test.yml)
 
-
 The front-end web app of Nextline.
 
 _Nextline_ is a DAQ sequencer of the [Observatory Control System
@@ -19,7 +18,6 @@ unless you need to refer to a specific package.
 
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.11451619.svg)](https://doi.org/10.5281/zenodo.11451619)
 
-
 ## Screenshot
 
 ![Screenshot](screenshot.png)
@@ -39,11 +37,15 @@ Docker images of the Nextline front-end web app are created as
 
 You can configure the web app in the container with these variables.
 
-| Environment variable | Default value           | Description                           |
-| -------------------- | ----------------------- | ------------------------------------- |
-| `PUBLIC_PATH`        | `/`                     | Path in the URL of the web app        |
-| `API_HTTP`           | `http://localhost:8000` | URL of the GraphQL API server         |
-| `API_NAME`           | `localhost`             | Text to be shown as part of the title |
+| Environment variable | Default value           | Description                                |
+| -------------------- | ----------------------- | ------------------------------------------ |
+| `PUBLIC_PATH`        | `/`                     | Path in the URL of the web app             |
+| `API_HTTP`           | `http://localhost:8000` | URL of the GraphQL API server              |
+| `API_NAME`           | `localhost`             | Text to be shown as part of the title      |
+| `SEED_COLOR`         | `#607D8B`               | The source color (hex) of dynamic colors\* |
+
+\*Accessible colors in light and dark modes are dynamically generated by
+[Dynamic Color in Material Design](https://m3.material.io/styles/color/).
 
 For example, if you are to run the web app at the port `8080` with the path
 `/nextline/` and use the GraphQL API server at `http://localhost:5000/graphql` as the name `API 1`, you can do so with the following command.
diff --git a/docker/config.json b/docker/config.json
index 71c2296..06ac627 100644
--- a/docker/config.json
+++ b/docker/config.json
@@ -1,4 +1,5 @@
 {
   "apiName": "localhost",
-  "apiHttp": "http://localhost:8000"
+  "apiHttp": "http://localhost:8000",
+  "seedColor": "#607D8B"
 }
diff --git a/public/config.json b/public/config.json
index 71c2296..06ac627 100644
--- a/public/config.json
+++ b/public/config.json
@@ -1,4 +1,5 @@
 {
   "apiName": "localhost",
-  "apiHttp": "http://localhost:8000"
+  "apiHttp": "http://localhost:8000",
+  "seedColor": "#607D8B"
 }
diff --git a/src/app/AppMain.vue b/src/app/AppMain.vue
index 6a1c30f..9f65cc8 100644
--- a/src/app/AppMain.vue
+++ b/src/app/AppMain.vue
@@ -38,9 +38,11 @@ stay hidden.
 -->
 
 <script setup lang="ts">
+import { computed } from "vue";
 import { useDisplay } from "vuetify";
 
 import { useProvideClient } from "@/graphql/urql";
+import { useConfig } from "@/utils/config";
 import { useColorTheme } from "@/utils/color-theme";
 import { useSetTitle } from "./set-title";
 import { useDrawer } from "./drawer";
@@ -49,8 +51,11 @@ import Banner from "./Banner.vue";
 import NavigationDrawer from "./NavigationDrawer.vue";
 import AppBar from "./AppBar.vue";
 
+const { config } = useConfig();
+const sourceColorHex = computed(() => config.value.seedColor)
+
 useProvideClient();
-useColorTheme();
+useColorTheme(sourceColorHex);
 useSetTitle();
 const { mobile } = useDisplay();
 const { drawer, toggleDrawer } = useDrawer();
diff --git a/src/utils/color-theme/color-theme.ts b/src/utils/color-theme/color-theme.ts
index 9e7c8ed..b0c360c 100644
--- a/src/utils/color-theme/color-theme.ts
+++ b/src/utils/color-theme/color-theme.ts
@@ -1,4 +1,5 @@
 import { ref } from "vue";
+import type { MaybeRef } from "vue";
 
 import { useDynamicColors } from "@/utils/dynamic-color";
 import {
@@ -7,14 +8,11 @@ import {
 } from "./monaco-editor";
 import { useDynamicColorsOnVuetify, useDarkModeOnVuetify } from "./vuetify";
 
-function useSourceColor() {
-  const sourceColor = ref("#607D8B"); // blue grey
-  // const sourceColor = ref("#E91E63"); // pink
-  return { sourceColor };
-}
+const DEFAULT_SOURCE_COLOR_HEX = "#607D8B"; // blue grey
+// const DEFAULT_SOURCE_COLOR_HEX = "#E91E63"; // pink
 
-export function useColorTheme() {
-  const { sourceColor: sourceColorHex } = useSourceColor();
+export function useColorTheme(sourceColorHex?: MaybeRef<string>) {
+  sourceColorHex = ref(sourceColorHex ?? DEFAULT_SOURCE_COLOR_HEX);
 
   const optionsLight = { sourceColorHex, dark: false };
   const optionsDark = { sourceColorHex, dark: true };
diff --git a/src/utils/config/ProvideConfig.vue b/src/utils/config/ProvideConfig.vue
index 48305d3..4059268 100644
--- a/src/utils/config/ProvideConfig.vue
+++ b/src/utils/config/ProvideConfig.vue
@@ -15,28 +15,8 @@
 /**
  * Load config asynchronously and provide it to the child components.
  */
-import { ref, watchEffect, nextTick } from "vue";
-import type { ComputedRef } from "vue";
 import { useLoadConfig } from "@/utils/config";
-import { useProvideConfig, Config } from "@/utils/config";
-
-const error = ref<Error>();
-
-const { error: loadError, config } = await useLoadConfig();
-watchEffect(() => {
-  error.value = loadError.value;
-});
-
-if (!config.value) throw new Error("Config is null");
-useProvideConfig(config as ComputedRef<Config>);
-
-// For test reactivity of loading.
-// await new Promise((resolve) => setTimeout(resolve, 1000));
-
-// For test reactivity of error.
-// error.value = new Error("Test");
-// nextTick(async () => {
-//   await new Promise((resolve) => setTimeout(resolve, 1000));
-//   error.value = undefined;
-// });
+import { useProvideConfig } from "@/utils/config";
+const { error, config } = await useLoadConfig();
+useProvideConfig(config);
 </script>
diff --git a/src/utils/config/config.ts b/src/utils/config/config.ts
index 8ce5469..bc661da 100644
--- a/src/utils/config/config.ts
+++ b/src/utils/config/config.ts
@@ -2,6 +2,7 @@ export interface Config {
   appName: string;
   apiName: string;
   apiHttp: string;
+  seedColor: string;
 }
 
 export const defaultConfig = {
@@ -18,4 +19,8 @@ export function validateConfig(config: Config) {
 
   if (typeof config.apiHttp !== "string") throw Error("apiHttp is not string");
   if (config?.apiHttp === "") throw Error("apiHttp is empty");
+
+  if (typeof config.seedColor !== "string") throw Error("seedColor is not string");
+  if (!/^#([0-9A-F]{3}|[0-9A-F]{6}|[0-9A-F]{8})$/i.test(config.seedColor))
+    throw Error(`seedColor is not a valid hex color: ${config.seedColor}`);
 }
diff --git a/src/utils/config/index.ts b/src/utils/config/index.ts
index c4ee90f..5be54db 100644
--- a/src/utils/config/index.ts
+++ b/src/utils/config/index.ts
@@ -19,8 +19,9 @@ export const useConfig = () => useConfigT<Config>();
  * Provide the config to the child components.
  * In the child components, use `useConfig` to get the config.
  */
-export const useProvideConfig = (config: MaybeRefOrGetter<Config>) =>
-  useProvideConfigT<Config>(config);
+export const useProvideConfig = (
+  config: Exclude<MaybeRefOrGetter<Config | null>, null>
+) => useProvideConfigT<Config>(config);
 
 /**
  * Read the config from the config file.
diff --git a/src/utils/config/provide-config.ts b/src/utils/config/provide-config.ts
index 7a2b987..f0e6bff 100644
--- a/src/utils/config/provide-config.ts
+++ b/src/utils/config/provide-config.ts
@@ -2,15 +2,36 @@ import { ref, provide, watchEffect, toValue } from "vue";
 import type { MaybeRefOrGetter, InjectionKey, Ref } from "vue";
 
 import { injectionKey } from "./key";
-
 /**
- * Provide the config of type `T` to the child components.
- * In the child components, use `useConfig` to get the config.
+ * Provides a configuration of type `T` to child components.
+ *
+ * This function creates a reactive reference to the config and provides it
+ * to child components using Vue's provide/inject system.
+ *
+ * @template T The type of the configuration object
+ * @param The configuration, which can be:
+ *        - A value of type T
+ *        - A Ref<T | null>
+ *        - A getter function returning T or null
+ *
+ * @remarks
+ * In child components, use `useConfig` to retrieve this provided config.
+ * The config will only be provided once it has a non-null value.
+ * Subsequent updates to the config (including to undefined) will be reflected
+ * in the provided reference, but will not trigger a new provide.
  */
-export function useProvideConfigT<T>(config: MaybeRefOrGetter<T>) {
-  const configRef = ref(toValue(config)) as Ref<T>;
+export function useProvideConfigT<T>(
+  config: Exclude<MaybeRefOrGetter<T | null>, null>
+) {
+  const configRef = ref<T>() as Ref<T>;
+  let provided = false;
+
   watchEffect(() => {
-    configRef.value = toValue(config);
+    const value = toValue(config);
+    if (value === null) return;
+    configRef.value = value;
+    if (provided) return;
+    provide(injectionKey as InjectionKey<Ref<T>>, configRef);
+    provided = true;
   });
-  provide(injectionKey as InjectionKey<Ref<T>>, configRef);
 }