I have heard of this before, especially from people who use lights for paramedic-type uses. As I understand it, the ability to "see" a person's skin colour tells you a lot about their true condition (blood loss, internal bleeding, etc.). Incandescent lighting apparently makes these changes stand out more than LEDs.
Photoplethysmography (PPG) machines used to determine local subcutaneous dermal blood perfusion use the same idea. Its now used in non-invasive blood gas monitoring also i.e. how pink or blue a SCBU baby is, but is a lot more accurate than a visual interpretation. This again works by measuring the back scattered light of infrared lasers from the skin surface. Scanning Laser doppler machines work on the same principle as the PPG machine but work over a larger area of the dermal surface giving a pictorial representation of the blood perfusion of that part of the body. Very useful for determining whether a BK or AK amputation is required due to the viability of the skin flap.
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