Added logic to color the border of the preview <div> in the opposite …

…color of that being previewed, for better contrast.

webpack_in/entry.jsx

@@ -305,12 +305,20 @@ class ColorSelector extends React.Component {
     render() {
         const { color } = this.state;
 
+        const colorOpposite = {
+            r: 255 - color.r,
+            g: 255 - color.g,
+            b: 255 - color.b
+          };
+
         return (
             <div style={ objStyleCommon }>
               <div style={{ margin: '1em auto',
                             width: '70%',
                             height: '3em',
-                            border: 'solid 2px black',
+                            border: `solid 2px rgb(${colorOpposite.r},
+                                                   ${colorOpposite.g},
+                                                   ${colorOpposite.b})`,
                             backgroundColor: `rgb(${color.r}, ${color.g}, ${color.b})`}} />
               <div style={{ marginTop: '-1em'}}>
                 <ColorComponentEntry label="R" value={ this.state.color.r } onChangeValue={