title: How to update datatable with formatStyle via dataTableProxy
body: <p>I am trying to update the <code>backgroundColor</code> of a column using a <code>dataTableProxy</code>. However, I am not sure of how to properly handle the column names. Here's an example :</p>
  
  <pre><code>library(shiny)
  library(DT)
  
  ui &lt;- fluidPage(
     fluidRow(
         DT::dataTableOutput("myplot")
      )
  )
  
  server &lt;- function(input, output) {
  
      output$myplot &lt;- DT::renderDataTable({
          datatable(as.data.frame(rnorm(5))) %&gt;%
              formatStyle(1, backgroundColor = 'red')
      })
  
      proxy &lt;- DT::dataTableProxy("myplot")
      mycolors &lt;- c("red", "green", "blue")
  
      observe({
          invalidateLater(1000)
  
          proxy %&gt;% replaceData(as.data.frame(rnorm(5)))
  
          # proxy %&gt;% replaceData(as.data.frame(rnorm(5))) %&gt;%
          #     formatStyle(1, backgroundColor = sample(mycolors, 1))
      })
  }
  
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p>Even though the numbers update as I would expect, I can't get the <code>formatStyle</code> to work (commented out code). It keeps showing the following error :</p>
  
  <blockquote>
  <pre><code>Warning: Error in !: invalid argument type
    56: name2int
  </code></pre>
  </blockquote>
  
  <p>And here's the error I get using <code>"rnorm(5)"</code> as column when calling <code>formatStyle</code>.</p>
  
  <blockquote>
  <pre><code>Warning: Error in name2int: You specified the columns: rnorm(5), but the column names of the data are 
    57: stop
  </code></pre>
  </blockquote>
  
  <p>What is the correct way of referencing the columns when using the <code>dataTableProxy</code> ?</p>