The billet is a simple rectangular shape like a brick or ingot, and in fact is sometimes shown with simply shading to imply rounded corners, quite a rare feature in the largely solid and geometric art of heraldry. Billetty then comes to mean “strewn with billets”, i.e. the field is covered with regularly spaced rectangles with large gaps between them A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Billet. This kind of patterning is known as a treatment, and there are no fixed colours, any combination may be used.