% PDF/A-1b:2005

\enabletrackers[structure.tags,backend.tags]

\setupbackend
  [format=PDF/A-1a:2005,
   intent=sRGB IEC61966-2.1, % use <info> entry here; otherwise problems with predefined default profile
   profile=sRGB.icc, % use <filename> here
   level=0]

\setuptagging[state=start] % needed even for 'b'-version

\setupcolors[cmyk=no]
\definecolor[rgbblack][b=0.01]
\definecolor[transtest][r=1,g=1,t=.5]

\starttext

\starttextcolor[rgbblack] % forced /DeviceGray causes problems; we need a trigger

Text is needed, otherwise tagging base entries are not applied.

\stopchapter

\stoptextcolor

%\startTEXpage
\hbox\bgroup
    \blackrule[width=1cm,height=1cm,color=red]
    \blackrule[width=1cm,height=1cm,color=green]
    \blackrule[width=1cm,height=1cm,color=blue]
    \blackrule[width=1cm,height=1cm,color=rgbblack]
    \blackrule[width=1cm,height=1cm,color=transtest]\hskip-.5cm
    \blackrule[width=1cm,height=1cm,color=transtest]
\egroup
%\stopTEXpage

\stoptext