Complex sentence: Dilution genes may modify the colouring, lightening the fur to a mix of cream and blue, lilac or fawn; and the markings on Tortoiseshell cats are usually asymmetrical.
Split into simpler sentences: Dilution genes may modify the coloring, lightening the fur to a mix of cream and blue, lilac or fawn. The markings on Tortoiseshell cats are usually asymmetrical.