Yes, it needs onion.
Roast 1 onion, (maybe add a little bit of rosemary) and then add the tomatoes, let them get soft and then blend everything together like in the recipe.

If you use fresh tomatoes like in the recipe, it will be more orange than red. If you want it red and a little bit thicker, you can add tomato-paste (or use canned tomatoes). Also, you can use some sweet pepper if you don't like it hot.