title: How to set up step color regions?
body: <p>With <code>levelplot</code>/<code>spplot</code> we can use <code>at</code> to define the color region range (min, max, interval). My question is: how can I use red for values greater than 29.5? </p>
  
  <p>This is my sample NCDF file --> <a href="https://onedrive.live.com/redir?resid=6FFDD661570C7D0A!1107&amp;authkey=!ADN3WPrRGws_fV0&amp;ithint=file%2Cnc" rel="nofollow noreferrer">download here</a></p>
  
  <pre><code> library (raster)
   r &lt;- brick('bali.nc', varname='TEMPERATURE', level=1)
  
   library(rasterVis)
   jet &lt;- colorRampPalette(
     c('#00007F', 'blue', '#007FFF', 'cyan', 'yellow', '#FF7F00', 'red', '#7F0000')
   )
  
   # First Figure - without at
   levelplot(r, layer=1, margin=F, contour=F, col.regions=jet)
  
   # Second Figure - with at
   levelplot(r, layer=1, margin=F, contour=F, col.regions=jet, at=seq(27.5, 29.5, 0.1))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/B2Y7i.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/B2Y7i.png" alt="Figure A"></a>
  <a href="https://i.stack.imgur.com/ky45U.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ky45U.png" alt="Figure B"></a></p>