In a large pot, mix the onion, tomatoes and all peppers. Stir in tomato sauce, paste and vinegar... then season with chili powder, Italian seasoning and salt. Bring to a boil over medium-high heat; reduce to low and simmer 1 hour.
In a small bowl, mix together cornstarch and water; stir into the salsa until thickened. Transfer salsa to sterilized jars, leaving 1/2 inch at top; seal. Heat jars in a boiling water bath for 15 minutes. Store sealed jars in the refrigerator. Enjoy!