two-coloured title

colours.r

require(ggplot2) 
require(grid)

element_grob.element_custom <- function(element, label="", colour="black")  {
  
  disect <- strsplit(label, "\\n")[[1]]
  N <- length(disect)
  fun <- function(ii, colour)
    textGrob(disect[ii], y=unit(N, "lines") - unit(ii-1, "lines"), gp=gpar(col=colour))
  grobs <- mapply(fun, ii=seq_along(disect), colour=element$colour, SIMPLIFY=FALSE)
  gTree(children=do.call(gList, grobs), height=unit(N, "lines"), cl = "custom_title")
}

# gTrees don't know their size and ggplot would squash it, so give it room
grobHeight.custom_title = heightDetails.custom_title = function(x, ...)
  x$height
# silly wrapper to fool ggplot2's slightly paranoid checks...
custom_title <- function(colour, ...){
  structure(
    list(colour=colour, ...), # this ... information is not used, btw
    class = c("element_custom","element_blank", "element") # inheritance test workaround
  )  
}

qplot(1,1) + ggtitle("first line\nsecond line") + theme(plot.title=custom_title(colour=c("red", "blue")))