Sift all the dry ingredients together in a large bowl. Beat the egg and food coloring, if using, together in another bowl. Once incorporated, add the cold water. Gradually, add the wet ingredients to the dry ingredients and mix thoroughly to remove any lumps. Set aside.
While the batter is resting, preheat the grape seed oil in a deep heavy skillet, over medium heat, to around 350 degrees F. Make sure, for safety, that the oil only comes 3/4 of the way up the pan.
Alternate the vegetables and tofu on the skewers to form a colorful stick of vegetables.
In a large shallow dish and the flour and season it with salt and pepper, to taste. Gently roll the tofu and vegetable skewers in the flour, coating it well and shaking off any excess flour. Dip the skewers into the tempura mix, and let the excess batter drip back into the bowl. Add the skewers to the hot oil, in batches if necessary, and cook until golden brown and crispy, about 3 to 5 minutes. Transfer to a serving platter and serve with a simple dipping sauce of soy sauce and chopped chives, if desired. Enjoy.
Different flour absorbs different amounts of liquid so be patient and add slowly.