BUG: Custom tooltip not rendering background

When implementing a custom tootltip, the background is only under the title and not the title and the body.

Example at https://codepen.io/anon/pen/zyMRdG

Expected that the background should be covering the whole tootip

The options section is as follows:

options: {
  tooltips: {  		
    custom : t => {
      if(t.labelTextColors) {
        t.titleFontColor = t.labelTextColors[0];         
      }    		      
      t.title = ['Hello'];
      t.body  = [{ lines: ['foo']}];
    }
  }
}

My reason for a custom one is to override the title color depending on underlying data. A workaround is just to set the color like above but then implement the title and label callbacks, but it should be possible to just update the custom tooltip model in one go I thought?

[LeeLenaleee]

Dont know how much work it is to make it into a plugin, but I think that renaming it to html or external from custom might be a good idea to make it more clear its not customization for the default tooltip.

[etimberg]

Closing since custom was renamed to external and released in 3.0.0-beta.12