#' Add transparency to a vector of colors
#'
#' Add a transparency factor to each color in a vector of color names, using alpha on a scale of 0-255. Adapted from http://stackoverflow.com/questions/8047668/transparent-equivalent-of-given-color.
#' @param color_names vector of color names to be modified.
#' @param alpha numeric, the alpha value, between 0 (completely transparent) and 255 (the original color). Passed to \code{rgb}.
#' @importFrom grDevices col2rgb
#' @export
#' @return a character vector of the same length as \code{color_names}
#' @usage make_transparent(color_names, alpha = 100)
make_transparent <- function(color_names, alpha = 100) {
new_colors <- col2rgb(color_names)
apply(new_colors, 2,
function(x) {
rgb(red = x[1], green = x[2], blue = x[3],
alpha = alpha, maxColorValue = 255)
})
}
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