Green*

SketchSystems.spec

Green*
  tick -> Yellow

Yellow
  tick -> Red

Red
  tick -> Green

SketchSystems_prototype.js

function light(color, is_illuminated){
  var attrs = {width: '20px', height: '20px', 'margin-left': '20px'};

  if(is_illuminated){
    attrs.backgroundColor = color;
  } else {
    attrs.backgroundColor = 'black';
  }

  return $('div', {style: attrs});
}

function render(model){

  var active_light = model.active_states[0].name;

  return $('div',
           light('Red', active_light === 'Red'),
           light('Yellow', active_light === 'Yellow'),
           light('Green', active_light === 'Green'));
}