ConTeXt: How to make color derivation acts like LaTeX xcolor package

a bit digging on the context mailing list excavated this syntax which seems to do color mixing. But the exact rules are a bit unclear and it would probably be a good idea to ask on the context mailing list if this syntax is still supported and where it is documentated:

\setupcolors[state=start]
\usemodule[tikz]

\definecolor[ColorA] [1.0(red)]
\definecolor[myred02][0.8(ColorA,white)] % 
\starttext
\tikz\node[fill=red!20]{abc};

\framed[background=color, backgroundcolor=myred02]
        {\color[white]{red!20} }
\stoptext

From the ConTeXt color manual: you can use

\enabledirectives[colors.pgf]

\definecolor[pgfcolora][red!50!blue]

\starttext
\framed[background=color, backgroundcolor=pgfcolora]
        {\color[white]{red!20} }
\stoptext