Fixed the background color when nodes in focus.

client/app/scripts/charts/nodes-chart-elements.js

@@ -2,6 +2,7 @@ import React from 'react';
 import classNames from 'classnames';
 import { connect } from 'react-redux';
 import { fromJS, Map as makeMap, List as makeList } from 'immutable';
+import theme from 'weaveworks-ui-components/lib/theme';
 
 import NodeContainer from './node-container';
 import EdgeContainer from './edge-container';
@@ -199,7 +200,7 @@ class NodesChartElements extends React.Component {
         className={className}
         key="nodes-chart-overlay"
         transform={`scale(${scale})`}
-        fill="#fff"
+        fill={theme.colors.purple25}
         x={-1}
         y={-1}
         width={2}