To cite Polychrome in publications use:

  Coombes KR, Brock G, Abrams ZB, Abruzzo LV (2019). “Polychrome:
  Creating and Assessing Qualitative Palettes with Many Colors.”
  _Journal of Statistical Software, Code Snippets_, *90*(1), 1-23.
  doi:10.18637/jss.v090.c01 <https://doi.org/10.18637/jss.v090.c01>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{Polychrome}: Creating and Assessing Qualitative Palettes with Many Colors},
    author = {Kevin R. Coombes and Guy Brock and Zachary B. Abrams and Lynne V. Abruzzo},
    journal = {Journal of Statistical Software, Code Snippets},
    year = {2019},
    volume = {90},
    number = {1},
    pages = {1--23},
    doi = {10.18637/jss.v090.c01},
  }