@Sai Tarun anand: SkywalkerPL is correct Yellow is not needed but only if you are using the pure + pure rule or Diamond breeding rules.
So, you can get Peacock by:
Breeding Yellow + Purple
Breeding two pure Purple type dragons together (Magic and Peacock). A similar effect can be achieved when breeding two pure dragons with the same minor type together if the Purple type is a component of that minor type. (This is true for Black, Cosmic, Royal, Champion and Zodiac.)
Breeding Diamond + Diamond
Breeding two parents that collectively contribute only the Purple and Diamond types. The Purple type can also be acquired from any minor type for which it is a component. (True for Black, Cosmic, and Royal.) Minor types that have been split from other minor types (such as Champion and Zodiac) can also contribute their component types to the type pool.