title: Change color for specific nodes in GGDAG
body: <p>I am trying to reproduce the following graph in R with GGDAG. <a href="https://i.stack.imgur.com/dbKAM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dbKAM.png" alt="enter image description here" /></a></p>
  <p>So far I am able to reproduce all nodes and arrows. However I do not know how to change the color of the &quot;U&quot; node and add the correspondent legend to the graph. Help is highly appreciated!See code for the uncolored DAG below.</p>
  <pre><code>library(ggplot2)
  library(ggdag)
  
  coord_dag &lt;- list(
    x = c(P = 0, X = 2, D = 2, Z = 2, U = 4, M = 4, Y = 6),
    y = c(P = 2, X = 0, D = 2, Z = 6, U = 0, M = 3, Y = 2))
  
  my_dag &lt;- ggdag::dagify(X ~ P,
                           Z ~ P, 
                           D ~ X + Z, 
                           M ~ D + Z, 
                           U ~ X, 
                           Y ~ U + D + M + Z, 
                           coords = coord_dag, 
                           exposure = &quot;D&quot;, 
                           outcome = &quot;Y&quot;)  
            
    
  ggdag::ggdag(my_dag) + 
    theme_dag()
  </code></pre>