Sizing up in a slip dress will give you a roomier fit that slenderizes your shape.
A black dress slenderizes and provides the most versatility.
It also absorbs light, so it slenderizes the figure.
While black slenderizes, red actually makes you look heavier so if you plant to go with red, choose a tailored cut to look your best.
If you want a plus size red dress that slenderizes, shop for darker reds or even maroons on the rack.