title: ggplot2: color individual words in title to match colors of groups
body: <p>I recently saw a line chart in the Economist where the <a href="https://www.economist.com/blogs/graphicdetail/2018/04/daily-chart-1" rel="noreferrer">title had colored words to match the colors of the groups used in the line chart</a>.  I was wondering how to do this with a ggplot2 object.  Here is some code to make a line chart with everything like the econimist article except the colored words in the title.  At the bottom I show the desired output.  </p>
  
  <p><strong>This question is not about theoretical ways to display this info (like directly labeling or a legend) but rather specifically about coloring individual words in titles.</strong></p>
  
  <pre><code>data &lt;- data.frame(
      group = rep(c('affluence', 'poverty'), each = 6),
      year = rep(c(1970, 1980, 1990, 2000, 2010, 2012), 2),  
      concentration = c(.125, .12, .14, .13, .145, .146, .068, .09, .125, .119, .13, .135)
  )
  
  library(ggplot2)
  
  ggplot(data, aes(year, concentration, color = group)) +
      geom_line(size = 1.5) +
      geom_point(size = 4) +
      scale_y_continuous(limits = c(0, .15)) +
      labs(
          x = NULL, y = NULL, 
          title = 'Concentration of affluence and poverty nationwide'
      ) +
      theme_minimal() +
      theme(
          legend.position = 'none'
      ) +
      scale_color_manual(values = c('#EEB422', '#238E68'))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/6eoab.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6eoab.png" alt="enter image description here"></a></p>