Grey squirrels can change colour slightly depending on the time of year. Their tails tend to turn a reddish brown and sometimes people even confuse them with red squirrels. Are they brown all year round? The DNA test will tell me if they are different to the average grey. It could be a slight mutation, like some grey squirrels can be white in the states.
The fresher the better, but hair samples have been shown to work even from museum specimens so they should be ok, I'll pm my details
These squirrels are dark brown all year round. Missus thinks she can find info,I'll post it later.s