Pink lights have recently appeared as a measure against teenage loitering, because they are supposed to highlight skin blemishes. When they were first installed by a resident’s association in Mansfield, UK in 2006, even though many sarcastic views were expressed in media, to the Mansfield residents it seemed like a cheap and doable solution.
http://news.bbc.co.uk/2/hi/uk_news/england/lancashire/6197652.stm
Blue neon lights were successfully used in public bathrooms and publicly accessible toilets, as a means of preventing drug users from injecting themselves. Because it makes veins harder to see, it is expected that drug users will stop using these bathrooms for the aforementioned purpose.
Blue lights used in the public toilet in The Hague City Hall; men's toilet
Blue lights used in the public toilet in The Hague City Hall; women's toilet
further reading:
http://www.theargus.co.uk/archive/1999/02/18/The+Argus+Archive/
http://news.bbc.co.uk/2/hi/uk_news/england/cambridgeshire/3147170.stm