Provides a comprehensive 'API' for colour conversion between popular
    colour spaces ('RGB', 'HSL', 'OKLab', 'OKLch', 'hex', and named colours) along with
    clean, modern 'CSS' Color Level 4 syntax output. Integrates seamlessly into
    'Shiny' and 'Quarto' workflows. Includes nearest colour name lookup powered by
    a curated database of over 30,000 colour names.
    'OKLab'/'OKLCh' colour spaces are described in Ottosson (2020)
    <https://bottosson.github.io/posts/oklab/>. 'CSS' Color Level 4 syntax follows
    the W3C specification <https://www.w3.org/TR/css-color-4/>.

Maps one of the viridis colour palettes, or a user-specified palette to values. 
    Viridis colour maps are created by Stéfan van der Walt and Nathaniel Smith, 
    and were set as the default palette for the 'Python' 'Matplotlib' library <https://matplotlib.org/>. 
    Other palettes available in this library have been derived from 
    'RColorBrewer' <https://CRAN.R-project.org/package=RColorBrewer> and 
    'colorspace' <https://CRAN.R-project.org/package=colorspace> packages.

Colour vision models, colour spaces and colour thresholds. Provides flexibility to build user-defined colour vision models for n number of photoreceptor types. Includes Vorobyev & Osorio (1998) Receptor Noise Limited models <doi:10.1098/rspb.1998.0302>, Chittka (1992) colour hexagon <doi:10.1007/BF00199331>, and Endler & Mielke (2005) model <doi:10.1111/j.1095-8312.2005.00540.x>. Models have been extended to accept any number of photoreceptor types.

Discover causality for bivariate categorical data. This package aims to enable users to discover causality for bivariate observational categorical data. See Ni, Y. (2022) <arXiv:2209.08579> "Bivariate Causal Discovery for Categorical Data via Classification with Optimal Label Permutation. Advances in Neural Information Processing Systems 35 (in press)".

Constrained ordinary least squares is performed. One constraint is that all beta coefficients (including the constant) cannot be negative. They can be either 0 or strictly positive. Another constraint is that the sum of the beta coefficients equals a constant. References: Hansen, B. E. (2022). Econometrics, Princeton University Press. <ISBN:9780691235899>.