All Moorish ornamentation is based on a strictly geometrical scheme, and every design may be resolved into a symmetrical arrangement of lines and curves at regular distances. The intersection of lines at various angles is the secret of the system. All these lines flow from a parent stem, and no figure or ornament is introduced at random. Moslem ornamentation abhors irregularity and rejects symbolism.
Simplicity and a love of the elementary characterize also the colouring of the decorations. On the stucco work only the primary colours were used: blue, red, and yellow. The secondary colours occur only in the dados of mosaic. The green groundwork of much of the ornamentation as it is to-day was formerly blue, time having changed the tint of the metallic pigment employed. The decoration of the surfaces seems to have been planned with strict regard to the coloring they were to receive. Both as regards decoration and colour.