A study has been carried out on Tawny Owls in Finland using 30 years of data relating to the colour of the owls in relation to climate change. There are two colour morphs found in the data, grey and brown and it is thought that more brown owls are monopolising the gene pool due to climate change.
The majority of owls have a dark mottled or streaky plumage to aid in camouflage and the Tawny owl is no different, I have seen Tawnies in Brown, Grey and a Rufous red morph. Being predominately nocturnal camouflage is a vital if they are to remain unseen during daylight hours. An owl of woodland here in the UK they are our most commonly found owl including towns and parks.
Take a look at the article below.