Add onAfterClose override to the ColorPickerDialog example

Add workaround for known issue opening multiple dialogs.

Author: johnguy0

docs/spfx/extensions/guidance/using-custom-dialogs-with-spfx.md

@@ -179,6 +179,13 @@ In the extension manifest, configure the extension to have only one button. In t
         isBlocking: false
       };
     }
+    
+    protected onAfterClose(): void {
+      super.onAfterClose();
+      
+      // Clean up the element for the next dialog
+      ReactDOM.unmountComponentAtNode(this.domElement);
+    }
 
     @autobind
     private _submit(color: string): void {
@@ -291,4 +298,4 @@ To associate the custom dialog box with your custom ListView Command Set, add th
 
 ## See also
 
-- [Overview of SharePoint Framework Extensions](../overview-extensions.md)
+- [Overview of SharePoint Framework Extensions](../overview-extensions.md)