posssible answers ....
1.) They are all lighthouses -
Longships and Eddystone are off Cornwall and Bishop's Rock is east of the Scilly Islands i.e. 'off' Cornwall .....
South Stack is off Anglesey ....
so 'location' may be the answer (i.e. South Stack because it is not 'off' Cornwall, and is in �Irish Sea� / not in English Channel !!
2.) Bryher / St. Anne's / Brownsea Island are all sites of lifeboat 'stations'.
White is not ( whether it is an Island of NZ does not matter! It is also a colour!)