title: Add a gradient fill to geom_col
body: <p>Here is come basic code for a column plot:</p>
  <pre><code>library(tidyverse)
  
  diamonds %&gt;%
    group_by(cut) %&gt;%
    summarise(
      count = n()
    ) %&gt;%
    ggplot(
      aes(
        x = cut,
        y = count,
        fill = count
      )
    ) +
    geom_col() +
    scale_fill_viridis_c(
      option = &quot;plasma&quot;
    )
  </code></pre>
  <p><a href="https://i.stack.imgur.com/d0Vbg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/d0Vbg.png" alt="basic col plot" /></a></p>
  <p>I could not find any examples of what I would like to do so I will try and explain it as best I can. I have applied a colour gradient to the fill aesthetic which colours the whole column plot one colour. Is it possible to have it such that each column of the plot contains the full colour spectrum up until it's respective value?</p>
  <p>By which I mean the &quot;Ideal&quot; column of my plot would look exactly like the key in the legend. Then the &quot;Premium&quot; column would look like the key in the legend but cut off ~2/3 of the way up.</p>
  <p>Thanks</p>