Which are the most caloric beers? Are there, say, visual criteria to identify them? Is there a visual criterion to roughly estimate the order of calories a beer contains?

Specifically, I wonder if "the darker the beer, the more energetic value it has" holds [1]. Please, prove or disprove.



[1] (What lead to this belief: When I drink a trappist or a Guinness Extra Stout, both dark, I somehow identify the density with calories. But is that true?)
No. Color has little to do with calories, and possibly surprisingly, mouthfeel can have little influence also.

You can have a Belgian Tripel that is medium light bodied, that has many more calories than a pint of Guinness, simply because the alcohol level in the Tripel contributes more calories than the sugars from Guinness. Also Guinness is served on Nitrogen which creates the sensation of a thicker beer, as if there were more carbs and protein giving a fuller body.

The calorific load from a beer comes from both carbohydrates and alcohol, which are present in both dark and light beers regardless of beer color.