Strega, strix and estrie are all synonyms for "witch", but also mean "owl".
Owls were known as "witches familiars" from achient Egypt, Rome and Asia, to modern Africa and Native America. They represent divine "Yin" or night, darkness, magic, sacred lunar and femine mysteries.
Owls are associated with both conventional and secret wisdom, such as WitchCraft, Magic, Sex, Death and Birth.
They are connected to Shamanism and are thought to bestow gifts of clairvoyance and teach the arts of astral projection; they serve as giuds to the realms of the spirits and the dead because of course they are proficient at navigating the darkness.
Owls are a significant symbol in the anchient naturist religions and at different times through out Earth's history were revered for their characteristic intelligence and feared for the thought that they were harbingers of bad luck or doom.
The colour of the owl would bear little significance on its meaning, but if you are following a path through Wicca or another naturist religion, you might see their appearance as an omen of acceptance in your pursuit.
Element Encyclopedia of WitchCraft - Judika Illes