The Bishop of Barf is prominent white painted rock high on a steep scree slope above the A66 by Bassenthwaite Lake. It's worth the scramble for the views. Scroll down for the Physics...
The clouds in the background are white (and grey) because they scatter all wavelengths of light. The Bishop is white because the paint reflects all wavelengths of light (apart from in the bit where some naughty person has sprayed "AMY :)" ) And note that the fields below don't reflect all wavelengths. The red and blue ends of the spectrum are reflected but the green is reflected.
