\documentclass[a4paper]{article}

\usepackage{pgfplots}

\usepackage{pgfplots.assert}

\begin{document}

%\tracingcommands=2\tracingmacros=2
%

\pgfplotscolornormalizesequence[colorspace=rgb]
\pgfplotscolornormalizesequencezero

\pgfplotsassertequalstok{0,0,0}{\pgfplotsretval}{zero is wrong}

\pgfplotscolornormalizesequenceaddweighted{\pgfplotsretval}{1}{1,1,1}
\pgfplotsassertequalstok{1.0,1.0,1.0}{\pgfplotsretval}{}


\pgfplotscolornormalizesequenceaddweighted{\pgfplotsretval}{2}{1,2,3}
\pgfplotsassertequalstok{3.0,5.0,7.0}{\pgfplotsretval}{}


\pgfplotscolornormalizesequence[colorspace=cmyk]
\pgfplotscolornormalizesequencezero

\pgfplotsassertequalstok{0,0,0,0}{\pgfplotsretval}{zero is wrong}

\pgfplotscolornormalizesequenceaddweighted{\pgfplotsretval}{1}{1,1,1,1}
\pgfplotsassertequalstok{1.0,1.0,1.0,1.0}{\pgfplotsretval}{}


\pgfplotscolornormalizesequenceaddweighted{\pgfplotsretval}{2}{1,2,3,4}
\pgfplotsassertequalstok{3.0,5.0,7.0,9.0}{\pgfplotsretval}{}
\end{document}

