You don't breed mantles to fawns or blues. So the answer is never if you don't cross color breed. I am not real savvy on Harl color genetics but only back yard breeders would do such a breeding in the first place. You can not get a fawn out of a Harl. You can get what is referred to as fawniquins (fawn patches instead of black) but a Harl or mantle can not produce a true fawn. A Harl that carries the blue gene then bred to a blue or a black carrying for blue could produce a blue. But again, those types of breedings are not done often or as the norm. The color code for breeding Danes can be found at www.gdca.org