So Why *Do* Our Veins Look Blue?

by Michael Mullaney on April 26, 2010

Check out our new story today on research from professor and vision visionary Mark Changizi.

An interesting tangent that emerged from my conversations with Mark, which he also addressed in the journal article, was the reason that human veins look blue when, indeed, we all know perfectly well that they’re filled with red blood.

Here’s what he has to say about it:

Our perception of blue-green veins depends crucially on its contrast with the surrounding skin. Blue-green veins if viewed all by themselves – i.e., through an aperture – do not appear blue-green at all. Veins are just slightly spectrally shifted toward blue-green compared to the skin’s baseline color, but when seen with the baseline color in the spatial surround, one sees the veins as genuinely blue-green.

So, our veins (and blood!) aren’t blue-green at all. It’s just that our eyes are hard-wired to see the contrast, however slight, of when a new color emerges against a background or “baseline” color. The slight blue-green tint of our veins is just greatly amplified against the expanse of our normal skin color. It’s all about context.

This relates directly to Changizi’s new study, which posits that hospitals outfit patients in nude-colored gowns and sheets, so doctors are better able to detect health-related skin color changes such as pallor or cyanosis.

Here’s the story in two pictures:

Another solution, Changizi says, are small “sticky notes” in a palette of different skin colors. The doctor would find the best color match to a patient’s skin, and place a number of these the sticky notes on the patient. If all is well, the sticky notes should be invisible – because they match the patient’s skin color. If the sticky notes stick out like a sore thumb, however, the doctor or nurse will know immediately that the patient’s skin color has changed.

Be sure to check out our news release, as well as this older story on Changizi’s book, The Vision Revolution. While you’re at it, read this excellent story, too: Uncovering the Human Superpowers.