I'm not sure if this is the "right" way, but one way is to include a vector of colors in your package. For example, I created a package with a bunch of utility functions and vectors that I use in my work. One file in the package is called utility_vectors.r where I keep various objects, one of which is a vector of my school's colors. An analogous version for your colors would be:
#' Vector of custom colors
#'
#' @examples
#' mycolors["my_orange"]
#'
#' @export
mycolors = c(
my_orange = '#ff6901',
my_purple = '#6f54a3',
my_green = '#53b647',
my_dark_green = '#118482'
)