Are there actual rules for the results of dragon crossbreeding?

Question

I recently acquired Fizban's Treasury of Dragons, because duh, dragons. It is the only 5e source book I own, although I have borrowed PHB, Xanathar's, Tasha's, etc from friends and family while building characters and playing in campaigns.

Frequently, usually in the "<age> <color> dragon connections" sections, Fizban's mentions dragons of various colors different from one another having romantic interests, making eggs together, raising hatchlings together, etc.

I was able to find one question that was looking for lore for dragon crossbreeds in 3.5e, and a few others from various non-5e versions related to applying half-dragon templates and so on to stat out the possible results, but I was curious if anywhere there are official (particularly 5e) rules for the offspring of dragons of non-same colors? Ie, do you get actual crossbreeds, do they inherit one parent or the other's type, and if so in what probability...and so on.

Obviously, one could house rule or home brew whatever they want (and if I were running a campaign, I probably would do just that), but I am curious if there are actual specific rules already in place.

Answer 1

Dragons are like lizards. They existed before humanoids and will exist long after them, they can manipulate reality’s fabric, and they transcend natural laws! Wait ... not like lizards. Ah! Like magic.

-Fizban

Sexual reproduction is only one of many methods in 5th Edition.

Fizban's Treasury of Dragons introduces some lore on dragon reproduction, but it is really more "worldbuilding guidance" than an answer to your question. The important takeaway for your question is that sexual reproduction that might produce mixed offspring is only one of a plethora of ways dragons reproduce across the multiverse:

Dragon reproduction varies from world to world in the Material Plane and can vary further depending on the family, kind, or individual nature of the dragons involved. Humanoids observing dragons have long assumed that their reproductive cycle resembles that of mundane reptiles—that two dragons of different sexes mate and produce a clutch of eggs. Sometimes, on some worlds, this is true, but dragon reproduction covers a wide range of other possibilities.

The Origin of Dragon Eggs table gives ten different ways dragon eggs can come to be without involving sexual reproduction, and gives no insight into mixing colors in this way. The point of Fizban's guidance here is "do whatever you want for your world and your story."

In this answer, Quadratic Wizard cites some relevant information from AD&D 2e; he writes:

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.