Short answer
In a living brain, the tissues appear pink with red blood vessels. Once the blood is removed, it becomes possible to create brain slices, showing that some areas are lighter in colour than others. These lighter regions have a higher concentration of myelin – a white substance that coats the long extensions of brain cells and facilitates fast communication between them.
Longer answer
From pink mass to white and grey matter
When untreated, the brain is a soft, pink mass with red blood vessels running through it. However, once the blood is removed, the tissues begin to decay, the brain becomes firmer, and various shades of grey emerge. But what distinguishes the lighter tissues from the darker ones? The darker tissue, referred to as grey matter, is made up of clusters of brain cells and their connections to other brain cells, known as dendrites. The lighter tissue, called white matter, consists of the long extensions of brain cells that carry electrical signals to other cells. These extensions are coated in myelin – a fatty, white substance that allows faster communication between cells. This white myelin gives the white matter its lighter appearance compared to the rest of the brain.
Left: An untreated deer brain.
Right: A brain after the blood has been removed.
Colourful brain images
Sometimes, images of the brain are often highly colourful, but these colours are not naturally present – they are artificially added. The most straightforward, colourful brain images typically illustrate brain anatomy for educational purposes. More complex images are often created using computer software, which assigns colours to microscopy or brain scan images. Vivid colours may also result from techniques, such as immunohistochemistry, that artificially stain specific molecules or cells.
Left: A colourful image of the brain showing different lobes.
Centre: A brain image created using ‘functional MRI’, where colour highlights areas of increased brain activity.
Right: A colourful image of a mouse brain produced by using artificial staining.
Image Sources:
https://commons.wikimedia.org, CC-BY-SA-4.0, https://commons.wikimedia.org/wiki/File:Gehirn_eines_Rehbocks_-_brain_of_a_roebuck.jpg
https://commons.wikimedia.org, CC-BY,
https://upload.wikimedia.org/wikipedia/commons/5/59/Human_brain_frontal_%28coronal%29_section_description_2.JPG
https://en.wikipedia.org, CC-PD-Mark, https://commons.wikimedia.org/wiki/File:Lobes_of_the_brain_NL.svg#filelinks
https://en.wikipedia.org, CC-BY-4.0, https://commons.wikimedia.org/wiki/File:1206_FMRI.jpg
https://en.wikipedia.org, CC BY-SA 4.0,
https://en.wikipedia.org/wiki/File:Coronal_section_of_a_mouse_brain_stained_with_Hematoxylin_%26_LFB.jpg