%./luatex -ini !
\input plain
\pdfoutput=1
\directlua0 {
   callback.register("define_font",
     function (name,area,size)
        if name == 'cmbx10-blue' then
            f = font.read_tfm('cmr10',size)
            f.name = 'cmbx10-blue'
            f.type = 'virtual'
            f.fonts = {{'cmr10', size}}
            for i,v in pairs(f.characters) do
                if (string.char(i)):find("[arthur]") then
                    v.commands = {
                        {'special','pdf: 0 0 1 rg'},
                        {'char',i},
                        {'special','pdf: 0 g'},
                    }
                else
                    v.commands = {
                        {'font',1},
                        {'char',i},
                    }
                end
            end
        else
          f = font.tfm_read(name,size)
        end
        return f
        end )
     }

\font\myfont = cmbx10-blue
\font\mono=cmtt10
\myfont Thank you Taco and Hans and Hartmut \mono:-)

\bye
