It is unlikely that pure barley, however strong the malting, will produce such a dark color. I think it is safe to assume that it is colored.
In Germany, this (or a very similar) beverage is called
Malzbier (See the English Wikipedia article on Malzbier) It is an alcohol free drink made with malted barley, and commonly colored with the food coloring E 150 (Look at the site of this popular drink, third FAQ item from the end). This is a coloring created by letting different types of sugar undergo a Maillard reaction, and can be considered a type of caramel. So it can be used in a malt drink in relatively high amounts without introducing an unusual taste or presenting a health risk.
If you have seen lighter barley water until now, this is probably because different producers use different amounts of coloring. It is probably a regional thing, the drink in the picture is produced in Spain, maybe they like their malted drinks darker.