Calluses typically appear yellow due to the accumulation of dead skin cells. When certain areas of the skin are subjected to repeated friction or pressure, the body's natural response is to thicken and toughen the skin in that area. This thickening occurs as a protective mechanism.
The accumulation of dead skin cells in the callus gives it a yellowish appearance. The dead skin cells can be more compacted and densely packed in calluses, leading to the yellow coloration.
It's important to note that calluses can vary in color depending on factors such as skin tone, thickness, and the presence of other substances like dirt or sweat. If you have concerns about a specific case of callus, it's always best to consult with a healthcare professional for a proper evaluation.