Changelings have an interesting relationship with gender as a concept, which is probably part of the reason a lot of the art doesn't find it necessary to distinguish the males with facial hair. As they're changelings though, they can have any kind of hair they want.
As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight, but not so much that your size changes.
Size. In their natural forms, changelings average between 5 and 6 feet in height, with a slender build.
The short version is that a Changeling can shapeshift to a form that can produce sperm to impregnate someone, and can shapeshift to a form with a uterus and eggs to get pregnant, but a pregnant Changeling cannot shapechange to a form without a uterus without ending the pregnancy.
Age: Changelings reach adulthood at the age of 16. Their fey heritage allows them to live much longer than humans, up to 200 years.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
While changelings can look like anyone, they do have a true form. Their natural look can be scary to some due to their lack of detail and distinctive features. Their skin tone is always pale, either white or light gray, and they tend to have slender bodies with limbs slightly longer in proportion to other humanoids.
As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
Changelings typically have large eyes with narrow pupils, ranging in color from white, to yellow, to black. Hair colors are similar: Light grey, platinum blonde, shades of silver, all the way to the darkest hair color being a light brown.
Changelings cannot alter themselves enough to change physical sizes (i.e, changing from Medium to Small, etc). It is worth noting that while a changeling could technically shift into something like an aarakocra, their wings would be non-functional.
Unlike doppelgangers, which are entirely genderless, a changeling does have a default gender that manifests in adolescence, but each changeling can adapt his or her form to be of either gender, hermaphroditic (both genders simultaneously), or entirely genderless.
A changeling is typically identifiable via a number of traits; in Irish legend, a fairy child may appear sickly and will not grow in size like a normal child, and may have notable physical characteristics such as a beard or long teeth.
Will a legless changeling regrow both legs when it copies someone? I say no. The changeling can change their coloration, hair length, sex, height, and weight, but they can't change their number, arrangement, or function of their limbs, because nothing in the feature says they can or even hints at it.
Appearance. In their true form, or their form "at rest", changelings have pale skin, colorless eyes that can be completely white or completely black, and white or silver-white hair.
Changelings have red blood like a majority of the other races. Bleeding around others may alert many that the Changeling is not of the same race (should the blood color vary). For this reason, a Changeling will usually choose to take the form of a race with red blood.
In their true form, changelings are generally extremely pale, showing features devoid of distinctive details, with colorless eyes and silver-white hair.
A changeling can eliminate or add traditional physical disfigurements - such as scars or birthmarks - when changing shape.
A changeling can alter its appearance. It can conceal existing scars or tattoos, or add new ones. So the tattoo will exist, but the changeling can hide it.
Changelings don't inherently recognize each other. If they don't want to be recognized then when they do something suspicious it would be an insight check against the changelings deception, which the changeling has advantage on. A changeling could have expertise in insight from divergent persona.
As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight, but not so much that your size changes.
Conversation. By RAW changelings revert when they DIE but not when they are unconscious (it would be hard to maintain a long term masquerade if you revert when you sleep!). I bet suggested that a piece of a Changeling — such as cut hair — WILL revert, but that this is slow and may take up to 24 hours.
Changelings are humanoid creatures with discolored, slimy skin, hollow eyes, and a round mouth with many teeth. They can appear human, but their true nature is revealed in their reflection.
Changelings need to sleep like everyone else after all and if they always reverted to their natural state when sleeping they would have one hell of a time staying hidden. A sleeping creature is considered unconscious in 5e at least.
Languages: Changelings begin play speaking the primary language of their host society and Common. Changelings who have high Intelligence scores can choose from among the following bonus languages: Aklo, Draconic, Dwarven, Elven, Giant, Gnoll, Goblin, and Orc.
Changeling Appearance
Their true skin is usually grey or pale white, and their facial features are blank slates to an unnerving degree. They're typically thin and gaunt, and their hair is usually silvery with an occasional green or pink tint.