|Green zentai suits are strange, but being dyed green from within is stranger (Source)|
When a person is unable to eat, a tube may be inserted down their throat in order to get nutrient-rich goop into their stomach. Dyes are often added to the goop to help healthcare workers ensure it doesn't accidentally end up in a patient's lungs. This unfortunate situation, otherwise known as pulmonary aspiration, can lead to pneumonia or, worst case, death by asphyxiation.
In one rather remarkable case, a woman being treated for multiple organ failure acquired an intense green skin colour while being tube fed a liquid meal containing Brilliant Blue FCF (FD & C Blue No. 1), a blue (surprise!) dye. The authors of the report describing the case suggested the greenness was the result of the blue dye becoming deposited in the woman’s skin, which had already taken on a yellowish color. Since her liver wasn't working properly, it wasn't able to effectively remove bilirubin, a yellow leftover from the breakdown of old red blood cells, leading to its accumulation in her blood and consequently a yellowing of her skin. The medical term for this is jaundice.
Beyond its use in tube food, Brilliant Blue FCF is often responsible for the colour of such fine consumables as blue raspberry ice cream, blue Curaçao (a citrus-flavoured liqueur), and blue mouthwash.
The dye can bind to pannexin 1, a common brain protein thought to be involved in debilitating conditions such as epilepsy and ischemic stroke, suggesting it might have some use as a drug down the road.
Brilliant Blue FCF has also been investigated for use during coronary artery bypass surgery where a vein is harvested from a person's leg and used to bypass a blocked up coronary artery to restore normal blood flow to their heart. During this surgery, surgeons use a surgical skin marker (containing gentian violet and isopropyl alcohol) to draw a line down the vein so they can properly orient it without twisting or kinking as they graft it onto a coronary artery. It appears using Brilliant Blue FCF instead of gentian violet results in less injury to a vein while it's being harvested and grafted. This is a big deal since vein graft failure is a serious concern after bypass surgery.
Czop M, Herr DL. 2002. Green skin discoloration associated with multiple organ failure. Critical Care Medicine 30(3):598-601.
Hocking KM, Luo W, Li FD, Komalavilas P, Brophy C, Cheung-Flynn J. 2015. Brilliant blue FCF is a nontoxic dye for saphenous vein graft marking that abrogates response to injury. Journal of Vascular Surgery (DOI: 10.1016/j.jvs.2014.12.059).
Wang J, Jackson DG, Dahl G. 2013. The food dye FD+C Blue No. 1 is a selective inhibitor of the ATP release channel Panx1. Journal of General Physiology 141(5):649-656. [Full text]