\setuppagenumber[state=stop]
\setupcolors[state=start]

\definecolor[colorA] [red]
\definecolor[colorB] [green]
\definecolor[colorC] [blue]

\newconditional\CondA
\newconditional\CondB
\newconditional\CondC


\unprotect

\def\GetStateDependentColor[#1]%
  {\bgroup
   \rawgetparameters[SDC@][A=,B=,C=,#1]%
   \def\MYdocommand##1%
     {\doifdefined{Cond##1} % conditional is known..
        {\expandafter\ifconditional\csname Cond##1\endcsname % ..AND true..
           \edef\CurrentColor{\csname SDC@##1\endcsname}\else
           \def\CurrentColor{}\fi
         \doifelsenothing\CurrentColor % ..AND a color is assigned
           \donefalse\donetrue}%
      \ifdone\CurrentColor\expandafter\quitcommalist\fi}%
   \processcommacommand[A,B,C]\MYdocommand % raw version does not work! why?
   \egroup}

\protect


\starttext

\setfalse\CondA
\settrue\CondB
\settrue\CondC

\tracingonline=1
%\tracingall=1
%\tracingmacros=1
%\tracingcommands=2
color is -\GetStateDependentColor[A=colorA,C=colorC]- % works so far
%\tracingmacros=0
%\tracingall=0

% crashes

%\tracingall=1
%\tracingmacros=1
%\tracingcommands=2
%\definecolor[testcolor][{\GetStateDependentColor[A=colorA,C=colorC]}]
%\color[testcolor]
%\color[{\GetStateDependentColor[A=colorA,C=colorC]}]
%\expandafter\color\expandafter[\expandafter{\GetStateDependentColor[A=colorA,C=colorC]}]
%\tracingall=0
TEST

\stoptext