diff --git a/.changeset/dry-spies-cover.md b/.changeset/dry-spies-cover.md
index 7006dee5c4..aae683faaf 100644
--- a/.changeset/dry-spies-cover.md
+++ b/.changeset/dry-spies-cover.md
@@ -3,4 +3,6 @@
 '@backstage/theme': patch
 ---
 
-Will Add warning variant to `DismissableBanner` component.
+Added a warning variant to `DismissableBanner` component. If you are using a
+custom theme, you will need to add the optional `palette.banner.warning` color,
+otherwise this variant will fall back to the `palette.banner.error` color.
diff --git a/packages/core-components/src/components/DismissableBanner/DismissableBanner.tsx b/packages/core-components/src/components/DismissableBanner/DismissableBanner.tsx
index 40082925c6..92b449f705 100644
--- a/packages/core-components/src/components/DismissableBanner/DismissableBanner.tsx
+++ b/packages/core-components/src/components/DismissableBanner/DismissableBanner.tsx
@@ -80,7 +80,8 @@ const useStyles = makeStyles(
       backgroundColor: theme.palette.banner.error,
     },
     warning: {
-      backgroundColor: theme.palette.banner.warning,
+      backgroundColor:
+        theme.palette.banner.warning ?? theme.palette.banner.error,
     },
   }),
   { name: 'BackstageDismissableBanner' },
diff --git a/packages/theme/api-report.md b/packages/theme/api-report.md
index 30dcb7b040..2dc6ab7b55 100644
--- a/packages/theme/api-report.md
+++ b/packages/theme/api-report.md
@@ -64,7 +64,7 @@ export type BackstagePaletteAdditions = {
     error: string;
     text: string;
     link: string;
-    warning: string;
+    warning?: string;
   };
 };
 
diff --git a/packages/theme/src/types.ts b/packages/theme/src/types.ts
index 40f45ee739..e1acba3a01 100644
--- a/packages/theme/src/types.ts
+++ b/packages/theme/src/types.ts
@@ -76,7 +76,7 @@ export type BackstagePaletteAdditions = {
     error: string;
     text: string;
     link: string;
-    warning: string;
+    warning?: string;
   };
 };