title: How do I change color of a bar in Vega-lite Bar Chart?
body: <p>I want to change the default blue color of a bar in a Vega-Lite bar chart. How can I do it? I am posting the json specification below:</p>
  
  <pre><code>{
   "data": {
   "values": [
    {"a":"A", "b":28}, {"a":"B", "b":55}, {"a":"C", "b":43},
    {"a":"D", "b":91}, {"a":"E", "b":81}, {"a":"F", "b":53},
    {"a":"G", "b":19}, {"a":"H", "b":87}, {"a":"I", "b":52}
   ]
   },
   "mark": "bar",
   "encoding": {
   "x": {bin:false, "type": "ordinal","field": "a"},
   "y": {"type": "quantitative","field": "b"}
   }
  }
  </code></pre>
  
  <p>Thanks in advance.</p>