Look for tri-tip roast that has a clear, red color. Beef normally is purplish-red, but when exposed to oxygen it takes on the cherry-red hue known as the "bloom." While the exterior is bright red, the interior of the meat retains the darker color. Vacuum-packed tri-tip roast also shows this purplish color. Packaged tri-tip roast should be cold and the packaging free of punctures or tears; vacuum-packed roasts should have the seal intact. The beef should be firm to the touch. Check the label for the "sell-by" date and make sure to buy it before or on that date