To cite package ‘gradientPickerD3’ in publications use:

  Peikert C (2017). _gradientPickerD3: Interactive Color Gradient
  Picker Using 'htmlwidgets' and the Modified JS Script
  'jquery-gradient-picker'_. R package version 0.1.0.0,
  <https://github.com/peikert/gradientpickerd3>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {gradientPickerD3: Interactive Color Gradient Picker Using 'htmlwidgets' and the
Modified JS Script 'jquery-gradient-picker'},
    author = {Christian D. Peikert},
    year = {2017},
    note = {R package version 0.1.0.0},
    url = {https://github.com/peikert/gradientpickerd3},
  }