title: how do you change the color of the cell in kable output table in knitr
body: <p>I need to color the cell if the value of the cell is greater than 80. For example, given this data frame called df:</p>
  
  <pre><code>dput(df)
  
  structure(list(Server = structure(1:2, .Label = c("Server1", 
  "Server2"), class = "factor"), CPU = c(79.17, 93), UsedMemPercent = c(16.66, 
  18.95)), .Names = c("Server", "CPU", "UsedMemPercent"), row.names = c(NA, 
  -2L), class = "data.frame")
  </code></pre>
  
  <p>df[2,2] should be in red color. I was able to change the color of the text by something like this using xtable:</p>
  
  <pre><code>df[, 2] = ifelse(df[, 2] &gt; 80, paste("\\color{red}{", round(df[, 2], 2), "}"), round(df[, 2], 2))
  </code></pre>
  
  <p>If I do this and print out the table with kable, it wont print out. Any ideas how can I color the cell in kable output table?</p>