Allergic to tomato what can be a substitute for cooking?

Tomatillos (or "Husk Tomatoes") can often be substituted for tomatoes. They are actually tropical berries and entirely unrelated to tomatoes, so your Allergies shouldn't be triggered by them; do not confuse them with green tomatoes, however, which are exactly as advertised: green tomatoes.

For tomato sauce, a blend of beet, carrot and onion puree can work well; the product "Nomato" markets several items using such a blend: ketchup, sauce, etc.