Different types of Italian marble like Botticino or Statuario will have various types of veins. It is up to the designer to choose the pattern of the veins in accordance to the marble lot that he has selected.
Interior designers today give their customers a computerised 3D design service view of the whole house to show them how the house is going to look once completed. In the 3D design service view, the homeowners can also check if the marble has diagonal or straight veins and they can choose accordingly.
The pattern of veins varies from stone to stone.
For example, in an Onyx Italian Marble, the diamond pattern looks good. Onyx Italian marble is translucent, so most designers see to it that there are lights placed behind the onyx marble. They try to make a feature in the house where Onyx is backlit, or they use Onyx on bar counter or maybe even on a dining table.
These are small little things make your home interiors look better.