I'm allergic to tomatoes and sometimes I've used other vegetable purees (think pumpkin/carrot/parsnip) if tomato is supposed to be a thickener. Part of the tomato is the acid flavor so I tend to supplement with a dash of citrus juice or vinegar. Since my difficulty isn't the acid, per se, I can't say that I've ever used tomato powder like what is sold in Hispanic groceries. That may be a way of adding tomato flavor without the acid content.

When I was a kid my mom cut the tomato content of marinara with grated zucchini; mild flavor without sacrificing body. Now I save all my tomato consumption for eating them in season fresh.

I couldn't eat acid for a while this summer, and someone told me about this. I've never tried it, but maybe someone else has?

http://www.nomato.com/index.htm

Do you think she could handle a puree of roasted red peppers? I'm not sure if they would be similar acidic. That's the first thing I'd try. Good Luck!

If you want something rich in flavor and red, maybe roasted peppers (cut up or even pureed)?

Tomato's often an ingredient included for acidity, though, and red peppers wouldn't do that.

I have the same problem and have making this fantastic pumpkin chili since I can't have traditional : http://www.skinnytaste.com/2011/10/crockpot-turkey-white-bean-pumpkin.html

I think it probably depends a lot on what you're trying to replace. I'd use different things in different recipes (the pumpkin chili looks really good, for instance!)

For pasta, I love Romesco Sauce - it's a roasted pepper sauce with a different flavor than tomato sauce, but it is our preferred sauce for gnocchi. (forgive me for linking my own recipe but as I google it, I realize many other versions use tomato instead of carrot: http://quipstravailsandbraisedoxtails.blogspot.com/2010/11/food-desert-project-romesco-sauce.html )

I'm going to try that nomato stuff. My hubby is really bothered by the acidity with his GERD.

As I have kidney problems, I have to avoid potassium. No tomatoes, no pumpkins. I really miss spaghetti sauce.

I would try homemade roasted red pepper puree. Just roast the red peppers in the oven, skin, puree in a blender, then reduce in a pan on the stove on low for a while. This way the puree will be thick like tomato paste. You can store it in the fridge for a 2-3 weeks or freeze in ice cube tray. I've been using that for soups, sauces and stews lately, just loving it. I too have issues with acidity, so red peppers is a good alternative for me. Store bought red pepper paste will often have acidity added to it, like vinegar, citric acids, and often hot spices. So I would avoid those if acidity is an issue. And I'd say, squash puree is a good alternative to tomato sauce.

Oh, and you can make a delicious red pepper pesto to use with pasta. Roast red peppers, skin, puree with one garlic glove, roasted pine nuts and romano cheese. You can use this pesto as a base to add to pasta with a bit of olive oil or with whole cream.

I second what Areana said! Definitely red peppers!

i have had several dishes including pizza with a butternut squash puree instead of tomato. yum.

definitely, as mentioned before peppers, though i find i quite time absorbing to roast them yourself or make your one puree, whereas in most recipes you just add a jar of tmoatoes.
if you can find it, try to get 'ajvar', a pepper and eggplant puree from the balcan, which comes in jars. i somerimes get pepper puree in jars (mild and hot) in turkish food shops; this can even be used as pizza topping or in any other tomatoe based recipe.
moreover, i recently stumpled over the use of tamarind paste (with water), but i haven't tried yet.

I'm allergic to tomatoes right down to tomato powder in seasonings. For dishes that call for salsa/tomato sauce I often substitute green salsa (made with tomatillos) and if it calls for ketchup I add molasses to copy the sweetness. For Indian dishes I've found that roasted squash is a great substitute for canned tomatoes. You can also find a lot of tomato free versions of recipes by doing a little searching - I found a great tomato free chili recipe just by searching. For pizza I go creamy (alfredo, garlic sauce) or oily (pesto, oil and herbs). Hope this helps!