Ada Countess of Lovelace 1815-1852 pioneer of computing lived here

Spudgun67 on Wikimedia Commons
Diane Griffiths on Flickr
Nick Harrison on Flickr
Spudgun67 on Flickr
Simon Harriyott on Flickr
Spudgun67 on Flickr
BluePlaquesGuy on Flickr
BluePlaquesGuy on Flickr
rebamex on Flickr
BluePlaquesGuy on Flickr
BluePlaquesGuy on Flickr
Simon Harriyott on Flickr
Spudgun67 on Wikimedia Commons
Simon Harriyott on Flickr

12 St James's Square, Westminster, SW1, London
Google Streetview

by English Heritage in 1992

Colour: blue

Wikimedia:

Flickr:

See also...
g0akh on Flickr
Chris Page on Geograph