Some sushi places serve white ginger flakes with their food, while others serve pink colored ginger. There doesn't seem to be any detectable taste difference that I've found. So, what is the difference between the two other than just color, and, why serve one over the other?
Although white ginger and red (or pink) ginger do exist, the different colors in sushi ginger are from a dye. The color in white sushi ginger comes from the pickling process and the red/pink color in ink sushi ginger comes from an artificial dye (usually E124 -cochineal red- or in other brands beet extract). The generic name for sushi ginger is gari and here's the Wikipedia page.
White gari/sushi ginger on the left and pink gari/sushi ginger on the right.
The bright pink ginger is pink because of food coloring.
Salt and acids (in the case of pickled ginger, vinegar and citric acid) turn ginger pink during the pickling process naturally. However, this hue will eventually fade to pale yellow and then brown in less than 3 months as the ginger gets exposed to UV light and heat. This is why food coloring is added to the pink variety. As for the yellow/white pickled ginger, sodium metabisuphite must be added to stop the product from turning brown. This sulphite is an allergen and must be accordingly labeled. If you want to preserve the natural pinkish hue of the pickled ginger, keep the product refrigerated at 2 degrees Celsius. Away from UV light and heat, the color will remain for up to 1 year.