In a pot over low to medium-low heat, combine the cubed Velveeta, 2 cups of milk, and butter. Melt slowly, stirring frequently, until completely smooth. Stir in the onion powder, garlic powder, black pepper, and smoked paprika. Remove from heat and let the sauce cool slightly.
In a separate bowl, whisk together the 1 cup of milk and eggs. Once the cheese sauce has cooled enough that it won't scramble the eggs, whisk the egg mixture directly into the cheese sauce. Stir in the half-and-half or evaporated milk. If you don't want to wait for it to cool, temper the eggs by slowly whisking small amounts of the warm cheese sauce into the egg mixture a little at a time before combining everything together.
Boil the elbow macaroni in heavily salted water until just tender. Drain well.
Preheat the oven to 350°F. Spread a layer of cooked macaroni across the bottom of a 9x13 baking dish. Spoon some of the cheese sauce over the pasta then sprinkle generously with freshly shredded Colby Jack and cheddar. Repeat — macaroni, cheese sauce, shredded cheese — continuing to layer until you reach the top of the pan. Finish with a generous layer of shredded cheese on top.
Bake at 350°F for 30 minutes until hot, bubbly, and golden. For an extra golden top, broil for a few seconds at the end watching closely so it doesn't burn.