Normally I'd say that large people really shouldn't wear intricate patterns, as they do make bodies look larger. Light, simple patterns are wonderful, they can even help accentuate larger people in a beneficial way. I also feel white, and light colors, aren't the best. Because white reflects light, it can make anything white appear larger. Black, on the other hand, absorbs light, and makes black objects appear smaller.
Large people can wear white and look great.
Its all in how you wear it. Look at Aretha Franklin in VH1's Divas concert. She looked wonderful. I'll admit its also because white is a very flattering color to those with darker skin. It does tend to enhance the richness of their skin color, creating a beautiful contrast that makes their appearance even more vibrant and alive.