Despite the name, the sauce is available all day but was created specifically to complement the savory items on their breakfast menu.
According to the chain, breakfast salsa is less spicy than Mild Sauce and features "notes of jalapeno" whereas Mild Sauce is "more chili-forward." The idea here seems to be for a slight heat without being "overwhelmingly hot." Of course, heat-seekers can still go for Diablo Sauce with their meal.
Photo via Taco Bell.