Boston's John Hancock tower recently got such a mural, visible from miles away: http://bcheights.com/metro/2015/mural-hancock-tower-public-art/ http://bcheights

Boston's John Hancock tower recently got such a mural, visible from miles away: http://bcheights.com/metro/2015/mural-hancock-tower-public-art/ http://bcheights.com/metro/2015/mural-hancock-tower-public-a... You don't need to block much light to do something like this. Blocking with a bright matte paint an amount of light equal to that which is normally reflected would be quite visible, and would not significantly impact the light entering the building. (This is because you don't normally see reflections of the sun off a glass building, but rather reflections of other buildings, which are matte surfaces. So e.g. a translucent matte mural which blocks 10% of sunlight would be nearly twice as bright as 10% reflections of matte buildings that reflect/scatter 50% of sunlight, while only reducing transmitted light by 10%, from 90% to 81%.)