Obviously, a changeling's appearance can change at any moment, but they do have a true form. 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.
The true form of a changeling is a bit paler than a typical human with slightly elongated limbs. Their eyes are colorless and ringed by black as pictured in the artwork above by Julia Zhuravleva. They have no body hair, but the hair on their head can be platinum, white, or silver.
A common way that a changeling could identify itself is through displaying unusual behaviour when it thinks it is alone, such as jumping about, dancing or playing an instrument – though this last example is found only within Irish and Scottish legend.
In their true form, changelings are generally extremely pale, showing features devoid of distinctive details, with colorless eyes and silver-white hair.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
Are they biologically asexual and just choose their current sex with shapeshifting? Yes. What's been stated in the past is that changelings set their sex with shapeshifting.
Changeling Appearance
Obviously, a changeling's appearance can change at any moment, but they do have a true form. Their true skin is usually grey or pale white, and their facial features are blank slates to an unnerving degree.
They have large colorless eyes circled by thick black rings. Their hair color is most commonly a light shade of silver followed by platinum and blonde. In rarer cases, their hair can be pale shades of green, pink, and blue. Similar to elves, changelings lack body and facial hair.
Though a changeling can appear as nearly any medium-sized humanoid, their natural appearance is that of a featureless humanoid, with pale skin and a face nearly bereft of characteristics.
Most changelings don't know they're changelings.
Though they may always feel somewhat different or removed from human life, most changelings are too young to understand who they truly are.
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.
Changelings have the unique ability to transform their body to look however they want, provided they keep the same arrangement of limbs they already possess. It is very rare to actually see a changeling in it's 'true' appearance. Even when disguised, changelings can instinctively recognize each other.
Changelings are typically born with female anatomy, but some prefer to maintain male primary and secondary sex characteristics once in control of this ability.
As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
According to legend, the abducted human children are given to the devil or used to strengthen fairy stock. The return of the original child may be effected by making the changeling laugh or by torturing it; this latter belief was responsible for numerous cases of actual child abuse.
Size. In their natural forms, changelings average between 5 and 6 feet in height, with a slender build. Your size is Medium.
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 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.
A changeling can't make the wings at all. If they had wings, like from a class feature or something, then they could look like an Aaracokra with wings because they will have those limbs at that point.
The fifth edition Changeling was originally introduced Eberron: Rising From the Last War, where Changelings are humanoids who can change their faces thanks to an ancestral gift from Eberron's deities, the Sovereigns.
Their are limitations to a Changeling's ability. While they can appear like any particular race, they can't imitate the appearance of another person without seeing them properly and a description (even a detailed one) isn't sufficient either.
In their natural form, a Changeling stands just over five feet tall with pale grey or white skin and thin, straw-like, white hair. They have small, pointed ears and disproportionately long limbs compared to those of humans, giving them a gaunt appearance.
It's not widely known, but one of the few ways one may determine that a person is, in fact, a changeling has to do with their hands. Changelings generally do not have the skill to replicate "life lines," and sometimes even fingerprints.
Changelings are largely equine in appearance but possess insect-like characteristics. Originally, they had black carapace-like coats, webbed manes and tails, blue reflection-less eyes (unlike their queen's), fangs, bent horns, jagged ears, insect-like wings, and holes in their legs.
There is nothing saying changelings don't have facial hair. but considering they can literally change their appearance at will, there's nothing stopping them from having it even if they didn't by biological default.