\setupcolors[state=start]
\starttext
%% SC colors %%
\definecolor [SCwhite] [r=1.0, g=1.0, b=1.0] 
\definecolor [SCblack] [r=0.0, g=0.0, b=0.0] 
\definecolor [SCblue] [r=0.0, g=0.0, b=0.75] 
\definecolor [SCred] [r=0.75, g=0.0, b=0.0] 

\definecolor [SCgrey] [r=0.376, g=0.376, b=0.376] 
\definecolor [SCgreen] [r=0.0, g=0.45, b=0.0] 
\definecolor[cirmaBlue] [r=.0,g=.2,b=.6]  

\defineframedtext
  [framedSC]
  [framecolor=cirmaBlue,
   strut=yes,
   offset=2mm,
   width=local,
   align=right]

\definetyping[SC][option=commands, 
tab=2,numbering=line,
                    before={\startframedSC},
                    after={\stopframedSC}]

\startSC
/BTEX{\color[SCred] //// an example starting with a comment}/ETEX
/BTEX{\color[SCgrey] ``this is a string''}/ETEX .postln ;

/BTEX{\color[SCgreen] \letterbackslash aSymbol}/ETEX  ;

/BTEX{\color[SCblue] ThisClassDoesNotExists}/ETEX  ;
\stopSC

\stoptext