Bicycling with purple finger syndrome
A strange malady strikes my hands on bicycle rides during the latter days of August. I call it purple finger syndrome.
The digits of my right hand suffer the worst, turning a deep bluish purple by the time I return home from a ride. It clears up after a shower, only to beset me again …
Source: http://www.bikingbis.com/2012/08/27/bicycling-with-purple-finger-syndrome/