Why does white vinegar taste better when at restaurants?
According to a quick search on Google, there are two other types of vinegar served in fish and chips shops along with malt vinegar. 

The first (and my best guess) is onion vinegar -- which is white vinegar that has been used to pickle onions. This is clear, but at minimum contains onions and salt, and perhaps sugar and other pickling spices. (I should note that the recipe I linked to uses malt vinegar to pickle the onions, but you could certainly achieve the same result with white vinegar.)

The second vinegar is actually called non brewed condiment, and isn't actually vinegar. It's ascetic acid, water, and a bit of caramel coloring. The coloring would make it brown, but it wouldn't have the malt flavor.