Heat oil in a large nonstick skillet over medium-high heat. Add onion and next 3 ingredients; cook, stirring constantly, 5 minutes or until crisp-tender. Add vinegar, saffron, and red pepper; cook 3 minutes or until vinegar evaporates.
Add tomatoes and next 3 ingredients; bring to a boil. Reduce heat, and simmer 15 minutes. Add clams; cover and cook 10 minutes or until shells open. Discard any unopened shells. Add mussels; cook 5 minutes or until shells open. Discard any unopened shells. Add shrimp and crabmeat; cook 4 minutes or until shrimp are done.