title: Is it possible to desaturate a ggplot easily?
body: <p>Is it possible to desaturate a <code>ggplot</code> easily? </p>
  
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  <p>In principle, there could be two possible strategies.<br>
  First, apply some function to a <code>ggplot</code> object (or, possibly, <code>Grob</code> object) to desaturate all colors. Second, some trick to print <code>ggplot</code> desaturated while rendering a <code>.rmd</code> file. Both strategies would be ok for me, but first one is, of course, more promissing.<br>
  Creating <code>ggplot</code> in greys from the beginning is not a good option as the idea is to have the same plot as if it was printed in shades of grey.   </p>
  
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  <p>There were some similar questions and remarkably good answers on how to perform desaturation in R. <a href="https://stackoverflow.com/questions/26314701/r-reducing-colour-saturation-of-a-colour-palette/26322593#26322593">Here</a> is a convenient way to desaturate color palette. And <a href="https://stackoverflow.com/questions/31800687/how-to-get-a-pixel-matrix-from-grayscale-image-in-r/31804561#31804561">here</a> is the way of desaturating a raster image. What I'm looking for, is a simple way of desaturating the whole <code>ggplot</code>. </p>