A unique and highly unusual new dragon offspring, who is typically sterile
The D&D 3.5 sourcebook Draconomicon (2003), p.27 asserts that dragons of different types can produce hybrid offspring:
Crossbreeds between dragon species are not unknown, but very rare. A hybrid dragon of this sort is usually left to fend for itself, but on occasion both parents (if they are on good terms with each other) might watch over it until it reaches adulthood.
The AD&D 2e Draconomicon (1990), p.64 describes that chromatic dragons can interbreed. The majority of such creatures are infertile, and therefore do not continue to produce offspring. Their coloration is a blend of the parents' color, and many other attributes are a half-way between the two parents, such as size and other details of physical appearance.
The breath weapon of a cross-breed dragon is usually that of one of its parents, but sometimes it is a combination of the two. They tend to learn the behavioural patterns of the parent who raises them.
The result of two metallic dragons breeding are more unpredictable and sometimes bizarre. These are rarer, with most interbreeding taking place between chromatic dragons (Draconomicon (1990), p.12).
Crossbreeds between metallic and chromatic dragons are extremely rare, but are known to happen. Their traits are highly variable and unpredictable, even more so than the offspring of two metallic dragons.
Bronze dragons particularly mate for life, and take courtship and mating very seriously, making a bronze hybrid less likely, but they care for their offspring with dedication. Blue dragons similarly have elaborate courtship rituals andcare for their eggs (Draconomicon (2003), p.40), so a hybrid between these two types of dragon may well survive to adulthood. The exact traits, however, are unpredictable.