Replace panel tileKey with a direct color prop.

Drop theme panelTiles keys and the ArticleView update callback wiring.

src/components/article/boxes/ArticleViewBrand.jsx

@@ -141,6 +141,7 @@ export default class ArticleViewBrand extends Component {
       <EditablePanelTile
         wide={1}
         minHeight={SECOND_ROW_MIN_HEIGHT}
+        color="#e9d5ff"
         value={value}
         onSave={this.handleSave}
         isDirty={brandDraftDirty}