\documentclass[a4paper]{article}

\usepackage{pgfplots}
\usepackage{pgfplots.assert}

\begin{document}

\pgfplotscolornormalizesequence[colorspace=rgb]

\pgfplotscolornormalizesequencenext{color=white}
\pgfplotsassertequalstok{1,1,1}{\pgfplotsretval}{}

\pgfplotscolornormalizesequencenext{rgb=1,0,0}
\pgfplotsassertequalstok{1.0,0.0,0.0}{\pgfplotsretval}{}

\pgfplotscolornormalizesequencenext{cmyk=0,0,0,1}
\pgfplotsassertequalstok{0,0,0}{\pgfplotsretval}{cmyk}

\pgfplotscolornormalizesequencenext{hsb=1,0.5,0.5}
\pgfplotsassertequalstok{0.5,0.25,0.25}{\pgfplotsretval}{hsb}

\pgfplotscolornormalizesequencenext{Hsb=360,0.5,0.5}
\pgfplotsassertequalstok{0.5,0.25,0.25}{\pgfplotsretval}{Hsb}

\pgfplotscolornormalizesequencenext{HTML=804040}
\pgfplotsassertequalstok{0.50195,0.25098,0.25098}{\pgfplotsretval}{HTML}

\pgfplotscolornormalizesequencenext{wave=500}
\pgfplotsassertequalstok{0,1,0.49846}{\pgfplotsretval}{wave}
\end{document}


