I know it is caused either by blood vessels beneath skin , or some pigment called "pheomelanin" . But what is it in fact?
The answer lies in hemoglobin, which is responsible for the transportation of oxygen throughout our bodies. It is the protein found in red blood cells, and thus it has a reddish hue to it. When an organism has lightly pigmented skin, the oxygenated hemoglobin causes the pinkish hue that you are describing.