utils/HtmlFonts.cc line 31:
  if (!(Ok(r)&&Ok(b)&&Ok(g))) {printf("Error : Bad color \n");r=0;g=0;b=0;}

Should be something like:
  if (!(Ok(r)&&Ok(b)&&Ok(g))) {
    if (!globalParams->getErrQuiet()) fprintf(stderr,"Warning : Bad color (%d,%d,%d), reset to (0,0,0)\n",r,g,b);
    r=0;g=0;b=0;
  }

As an error it should be written to stderr,
it should obey the -q switch,
if you continue it's a warning,
and it should give all the info available