In a large saucepan, combine the bell peppers, Anaheims, sugar, vinegar and salt and bring to a boil. Simmer over moderately high heat, stirring occasionally, until the peppers are softened, 20 to 25 minutes.
Increase the heat to high and quickly stir in the pectin. Boil for 1 minute, then remove from the heat. Using a wooden spoon, stir the mixture just until the foam subsides, then immediately ladle the jelly into a heatproof bowl or jars. Let cool completely, then cover and refrigerate until set, at least 12 hours.