How does Mars get its red color?
Hemoglobin
Historically, an association between the color of blood and rust occurs in the association of the planet Mars, with the Roman god of war, since the planet is an orange-red, which reminded the ancients of blood. Although the color of the planet is due to iron compounds in combination with oxygen in the Martian soil, it is a common misconception that the iron in hemoglobin and its oxides gives blood its red color. The color is actually due to the porphyrin moiety of hemoglobin to which the iron is bound, not the iron itself, although the ligation and redox state of the iron can influence the pi to pi* or n to pi* electronic transitions of the porphyrin and hence its optical characteristics.
Chestnut (coat)
Red hair color in horses ("e") is created by a missense mutation in the code for MC1R, which results in a protein that cannot bind to the Melanocyte-stimulating hormone (MSH), which is released by the pituitary gland, and stimulates the production and release of melanin in skin and hair. So long as one functional copy ("E") is present, the protein is formed normally and black pigment is produced. However, when only mutant copies ("e) of the gene are available, non-functional MC1R proteins are produced. As a result, no black pigment is deposited into the hair and the entire coat is red-based. However, the skin of chestnut horses is still generally black, unless affected by other genes. Some chestnut foals are also born with lighter eyes and lightened skin, which darken not long after birth. This is not the same as the blue eyes and pink skin seen at birth in foals carrying the champagne gene. It is a genetic mechanism not fully understood, but may be related to the pheomelanistic characteristics of "e".
The recessive nature the chestnut or "red" coat in horses occurs because a single copy of the "E" allele is dominant over the "e" allele. Therefore, for example, bay and black horses may be heterozygous for "e" and if so, could produce a chestnut foal when bred to another horse with at least one copy of "e". However, all chestnut horses are homozygous for the "e" allele and thus breeding a chestnut to another chestnut will always produce a chestnut foal. Thus, unlike many coat colors, chestnut can be true-breeding; if any color other than chestnut occurs, then one of the parents was not chestnut.