What can be used as a substitute for tomato sauce in typical italian dishes? I have a friend that has developed an allergy or sensitivity of some kind to tomato sauce in foods. She has been craving pizza, pasta, and lasagna for a while now and I've been searching for a way to make those sorts of dishes without using tomatoes, but while maintaining a similar flavor i.e. not a white sauce flavor.

Any ideas suggestions?
You could use Red Pepper Coulis:

Roast red peppers on grill, gas flame or cut off the sides and place skin side up under broiler until skins are blackened.  Cool and remove charred skin.

Sweat onions and garlic in a little olive oil with salt and pepper until softened.  Add the charred roasted red peppers and some chicken stock.  Simmer until vegetables are very soft and puree with an immersion blender, food processor or regular blender.  Taste and adjust seasoning as necessary.  Thin with additional stock according to consistency desired/needed.

Add basil, oregano, Italian seasoning blend to season as desired.