What you're referring to as "Napoli" sauce sounds a lot like marinara, or a plain tomato sauce (no meat or fish). It's an extremely personal thing amongst Italians.
Here are my observations and beliefs. Bear in mind, my dad moved to the USA from Naples ("Napoli") when he was 24 years old.
* There is not now, nor ever will there be, sugar in tomato sauce. This is an abomination in most Italian households. It's a "shortcut" to cover up lousy tomatoes. If the tomatoes are bad, have pesto, have white clam sauce, but don't doctor up tomato sauce with sugar.
* There are two schools of tomato sauces. The long-cooked and the very briefly cooked. Plain tomato sauce can be cooked very briefly and one of the benefits of this method is the brilliant red color to which you refer. Yes, more intensity of flavor and thickness can be achieved by adding tomato paste but I only do this when I'm making a meat sauce. Meat sauces are generally longer-cooked but even this is personal. My mom had a friend who cooked her gravy so long it could take the paint off a Buick. This is not necessary and yields a highly acidic product which will have your family reaching for the Rolaids. Cooking time of one hour is sufficient after all the meat has been pre-sauteed and added to the saucepan.
* Buy ONLY whole-peeled tomatoes. Chopped, crushed, diced, pureed or sliced tomatoes are ways for manufacturers to sell less than top quality tomatoes. As my dad says, "If you had a perfect tomato, would you crush it to sell it??" I've got to agree. Stewed tomatoes are another thing - they are perfectly fine to use in certain recipes. They're just cooked prior to canning. That stuff they call "tomato sauce" in cans is absolute garbage. Avoid that at all costs.
Tomato sauce is very versatile and can be your best friend on a busy weeknight. Find your favorite techniques and you'll never be caught short as long as you have a can of tomatoes in the house.