\startluacode
  pgfutil = pgfutil or { } 
  local texsprint, format = tex.sprint, string.format
  local prtcatcodes = tex.prtcatcodes

  function pgfutil.unsupported_color(name)
    texsprint(prtcatcodes,format("\\PackageError{pgf}{color %s has unsupported model}{}", name))
    texsprint(prtcatcodes,format("\\pgfutil@definecolor{%s}{gray}{0}", name))
  end

  function pgfutil.registercolor(name, attributes)
    print(name, attributes)
    local cv = colors.value(attributes) 
    if cv then
      local model = cv[1]
      if model == 1 then
        print("model=1")
        texsprint(prtcatcodes,format("\\pgfutil@definecolor{%s}{gray}{%1.3f}", name, cv[2]))
      elseif model == 3 then
        print("model=2")
        texsprint(prtcatcodes,format("\\pgfutil@definecolor{%s}{rgb}{%1.3f,%1.3f,%1.3f}", name, cv[3], cv[4], cv[5]))
      else
        print("no model")
        pgfutil.unsupported_color(name)
      end
    else
        print("no color")
      pgfutil.unsupported_color(name)
    end
  end
\stopluacode

\unprotect
\def\pgfutil@registercolor#1%
  {\ctxlua{pgfutil.registercolor("#1",\thecolorattribute       {#1})}}
\protect