Typically associated with Halloween, witchcraft, and poor luck, black cats have long been thought of as related to witches, due to superstitions that came about in the Middle Ages. Thankfully, there are more positive myths around black cats, like them bringing better love to your life or improving your financial situation. Regardless of your stance on black cats, there's no doubt that these mysterious felines have no problem building curiosity for humans.
Why Black Cats Look Different in the Sun
Black cats often have a tabby pattern, but it's not always suppressed. In fact, it's common for black cats to have faint markings in certain lights. For example, many black cats experience a "rust" in the sunlight, where their coat turns a lighter brownish shade.
Even the blackest of black cats can look different in the sun. This can be partly due to feline genes. Cats' bodies, like humans, are made up of genetic materials, called genes. Genes and their associated alleles are responsible for the color of our eyes, the pigment of our hair, and other inherited physical traits from our forebears, such as long legs.
Additionally, the melanin in cats' hair is what determines the difference in the colors of eyes, skin, and hair. Melanin in the hair shafts and takes the form of microscopic granules, which vary in shape, size, and arrangement. This can be one of the reasons there is a variety of color in black cats' coats.
Recessive Genes in Cat Hair
Genes can be dominant or recessive. This is how a very black cat may appear as a brown cat in the summer sun—as a possible result of a recessive red gene. This is especially common in longhaired black cats. You may also have seen black cats with white roots, which are called "smokes."
It is believed that the original color pattern of all domesticated cats is the tabby. With this theory, most cats today carry the recessive gene for a tabby. However, solid colored cats (including black cats) have another recessive gene that suppresses the tabby pattern. If the tabby pattern is not completely repressed, this can be a reason for seeing a hint of tabby markings in a black cat under a bright light. The tabby "M" is the most distinctive of these.
The Cat Might Not Be Black
It's possible that the cat you're seeing in the sunlight is not black to begin with. Although the rarest color of cat is fawn, a dilution of cinnamon most commonly found in Abyssinians, it's possible that you're seeing a yellowish-brown colored cat of this nature.
There are also mutations of the black colored coat, like chocolate. This often creates that summer brown hue on the coats of black cats. However, there are true chocolate-colored cats all year round, most notably in Havana Browns and Persians. Additionally, there are colored variations in solid black cats, including coal black, grayish black, and brownish black.
Source: Cat Color Genetics