Myoglobin
The protein in dark meat that gives it its deep red color. When the meat reaches a certain temperature, the protein goes through several steps of denaturation and oxidation, whereby it loses its color, and the meat will change color to be brown. This transformation is often used by color normals to tell when meat is done cooking, but is difficult for the red-green colorblind since the before and after colors lie along a confusion line.
![](https://chromaphobe.com/wp-content/uploads/2022/01/CHROMATICITY.png)