How does beer cause dehydration if your urine is the correct color as the chart at work?

Where I work there are color charts for urine on the wall behind the urinal. You compare your color of urine to the chart and based on the color it states how hydrated or dehydrated you are. If I am drinking beer and my urine is the color of the “hydrated” section then how does beer make a person dehydrated? It’s mostly water.