This is true. It has to do with how storms move and how the low sun reflects lights on clouds. When there is a storm system there are clouds. When the low sun hits the water droplets in the clouds it fractures into more reds and oranges hence a red sky. Storms typically move from west to east. So the setting sun turns the sky red when the storm is moving away from you giving clear conditions the next day. But when the sky is red in the morning it's hitting the storm clouds that are coming towards you brining more of a weatherly day.