Evidence of Viking Shield Patterns and Colors

Viking shields are commonly portrayed as brightly colored and highly stylized. How is it that we have come to conclusion. The following is a list of all evidence I can find as to the reconstruction of how Viking shields looked.

• The "Gokstad ship" was found in Norway and 32 shields lining each of the gunwales. They were painted alternately in black and yellow.  This is the only evidence of colorful shields. 

Runestone carving, from Gotland (Sweden). It clearly depicts a "pinwheel" pattern emanating form the shield boss. There also appears to be a rim on the shield. Archeologists suspect rawhide, as there is unsubstantial evidence to suggest iron.

The Tangelgarda Stone, from Gotland.