Change color of x label in a panel under facet_grid?

[jarjarbinks]

I need to change the color of U treatment only to red, but I end up having the following figure. I attempted to change the color of the first x label using axis.text.x = element_text(color = c("red", "black", "black")) but it seems that every first element in the panel will also change color to red. I only want the change of color happen in the first panel.

Here's the code for the figure:

x = ggplot(stmraw.csv, aes(x, y, fill=group)) +
      theme_classic() + labs(x = 'Labels', y = 'Index') +
      geom_boxplot() + facet_rep_grid(.~group, scales = 'free_x', ) +
      scale_fill_manual(values=color_scheme) +
      theme(legend.position="none",
            strip.background = element_blank(),
            strip.text.x = element_text(size=12),
            axis.line.y = element_line(colour = 'black', size=0.5, linetype='solid'),
            axis.text.x = element_text(color = c("red", "black", "black")) ## Attempt to change the color of the first  x label
      ) +
      scale_y_continuous(breaks = c(0, 0.25, 0.50, 0.75, 1))

Thank you!

[mara]

Check out this response to a similar question on StackOverflow, which uses the ggtext package:

customize ggplot2 axis labels with different colors

I don't know what your data look like, but I imagine you could use a mutate() that defines the span color conditioned on the value of x (e.g. x == 'U'), and accomplish what the OP in that StackOverflow thread was trying to do based on a value of y.

I think that using the answer that suggests a vector of values to axis.text.x (as you've done above), will result in what you've already seen (the application of that vector across the various facets).