Pour the warm water into a medium bowl, stir in 1/2 tsp of the sugar, and sprinkle the yeast on top. Cover with a dishcloth or plastic wrap and leave in a warm place to proof for 5 minutes. After 5 minutes, the yeast should be foamy and fragrant. If it isn’t your yeast may not be active or the water may have been too cool or too warm.
Meanwhile, in the bowl of a stand mixer, whisk together the remaining 3 tbsp of sugar, the salt, and 3 cups of the bread flour. Place the bowl on the stand mixer fitted with the dough hook. Stir the oil into the yeast mixture, then pour into the flour mixture and beat until smooth. As the mixer runs on medium-low speed, add 1/2 cup or the remaining flour at a time until a soft dough is formed.
Turn the dough out onto a lightly floured surface and divide into 4 or 6 equal portions, depending on how many colors you want in your bread. Work with one piece of dough at a time and keep the others covered with a dishcloth or plastic wrap. Put on your gloves and add a drop or two of food coloring to your first piece of dough. Knead for 5-7 minutes or until smooth and elastic and the color is well distributed. Transfer the dough to a lightly oiled bowl and turn once to coat the surface of the dough with oil. Cover with a dish cloth or plastic wrap. Repeat with the remaining pieces of dough with remaining colors. Allow all pieces to rise in a warm place until doubled, about 1.5-2 hours.
When the dough pieces have risen, turn out the first color of dough onto a lightly floured surface and pat out to a ¼-½” thick disk (like a pizza dough!) This first color will be the outside of your loaf. Pat out the next color into a disk on top of the first disk. Repeat with all remaining colors.
When all of the colors have been patted out, roll all the disks together, fairly tightly, to form your rainbow spiral loaf. Cut the loaf in half crossways to form 2 loaves. Transfer each loaf to a greased 9 x 5 loaf pan, cover, and let rise in a warm place until doubled, 1-1.5 hours.
Bake the loaves at 375F, about 30-35 minutes, or until lightly browned and the bread sounds hollow when tapped.
Remove from pans and allow to cool on wire racks. Cool completely before slicing for the neatest slices.