fixed bug where if backgroundColors initial value was not set

Author: shafy

src/SketchField.jsx

@@ -453,6 +453,9 @@ class SketchField extends PureComponent {
 
         this._initTools(canvas);
 
+        // set initial backgroundColor
+        this._backgroundColor(this.prop.backgroundColor)
+
         let selectedTool = this._tools[tool];
         selectedTool.configureCanvas(this.props);
         this._selectedTool = selectedTool;