• Lucille Solomon

Colour Codes in medical illustration

Medical illustration is usually used as an explanatory supplement to a text, which can not express the desired content purely in written form. It has the task of making a fact visible and understandable in the most effective way possible. The balance between correct content, objectivity, aesthetics, abstraction and detail is a major challenge in the creation of medical illustrations. Because there are only a few distinct colour contrasts in the human body the differentiation of different anatomical structures is not always easy. Especially if they are not recognizable by a distinctive shape or texture. Therefore, colour coding has been an important factor ever since the beginning of coloured medical illustration. The colours red and beige predominate in human anatomy so that the differentiation of the structures is difficult. A good medical illustration is characterized in that the types of tissue depicted can be clearly and quickly distinguished.

Different shades of beige and gray for bony structures.

The colour associated with a tissue type is usually ajar against the real tissue colour. Muscle tissue becomes reddish and bony structures appear beige, which corresponds to the actual colour tones. In contrast, arteries are usually depicted in saturated red and veins are shown in rich blue. But why were two striking colours chosen for these two vessels? One speculation is that, because of their shape, these closely spaced webs are difficult to assign so a bright colour contrast is the only distinguishing feature. Other reasons that are based on reality, why red is used for the arteries is because they contain oxygen-saturated blood, which is brighter and thus redder. In the veins, on the other hand, oxygen-poor blood flows, which thereby appears darker and bluer. If one compares these to the fibrous structure of the muscle tissue, which would be determined only by its texture, it can be assumed that, especially in the case of anatomical structures, which do not have many characteristic features regarding shape, position or texture, dominant color conventions are applied, that usually aren’t realistic. The variation of the shades of the same types of tissue, between the different anatomy books, also verifies this theory. Thus, nerve tracts that run in narrow lanes alongside other similar appearing lanes, are shown in a yellow tone which hardly ever varies. By contrast, the large intestine, which is characterized by its distinctive position and shape and can also be determined in monochrome representations, seemingly has less clear colour conventions.

Different shades of red, pink and brown.

There is an interesting theory regarding the colour coding of the muscles. The colour used for muscles often varies from pinkish red, to orange and even red-brown. The latter might be because meat oxidizes in the air and then turns brownish. And since there are fewer conflicts with the red arteries, there is an advantage of colouring the muscles in a reddish brown or a very light pink rather than a bright red. It’s an advantage if colour choices are discussed between the artist, client and/or the medical professional at the beginning of a project. Especially in bigger projects where colour coding should be consistent thought out. In conclusion:

  • Colour codes in medical illustration associated with a tissue type are usually ajar against the real tissue colour.

  • If anatomical structures don't have many characteristic features regarding shape, position or texture, colour codes are applied, which usually aren't realistic.

  • Deciding and discussing on a consistent colour code at the beginning of a bigger project.

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