#' vertex for the tetrahedral color space
#'
#' internal data for plotting devices.
#'
#' @name ttvertex
#' @docType data
#' @author Rafael Maia \email{rm72@@zips.uakron.edu}
#' @references Stoddard, M. C., & Prum, R. O. (2008). Evolution of avian plumage
#'   color in a tetrahedral color space: A phylogenetic analysis of new world
#'   buntings. The American Naturalist, 171(6), 755-776.
#' @keywords data internal
NULL
