Why were Viking sails red and white?

Why were Viking sails red and white? Fragments of Viking sails have been discovered and it appears as though Vikings made their sails with wool or linen, and they would often be dyed blood red for a more fearsome appearance. There have been numerous finds which do support the square rigging.

Fragments of Viking sails have been discovered and it appears as though Vikings made their sails with wool or linen, and they would often be dyed blood red for a more fearsome appearance. There have been numerous finds which do support the square rigging.