To cite package ‘ggnewscale’ in publications use:

  Campitelli E (2024). _ggnewscale: Multiple Fill and Colour Scales in
  'ggplot2'_. R package version 0.5.0.9000,
  https://github.com/eliocamp/ggnewscale,
  <https://eliocamp.github.io/ggnewscale/>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {ggnewscale: Multiple Fill and Colour Scales in 'ggplot2'},
    author = {Elio Campitelli},
    year = {2024},
    note = {R package version 0.5.0.9000, 
https://github.com/eliocamp/ggnewscale},
    url = {https://eliocamp.github.io/ggnewscale/},
  }