You may be overthinking this. There is nothing wrong with the plain and simple color. You can just say the skin is brown or green or purple without going all fancy about it.
As in:
He was warm and naked. Her hands fumbled with the edges of his robe, opening it upward, across his shoulders, deciphering the message of dark hairs and brown skin and the ridges of bone and muscle that were the body of Guillaume LeBreton.
The other Jacobin, pale skinned and pockmarked, followed, bearing a luxuriant mustache.
Gracefully, she reached up and stripped her fichu off her shoulders, unwinding it from her in a circle, uncovering white, white skin. The sun percolated through the trees to land in coin-shapesd drops all over her.
You can compare the color of the skin to something else -- preferably something that is evocative of the character.
As in:
LeBreton was earth brown. His hat, his clothing, even his skin were the dun and buff of the trees around them. He would be invisible in this corner of garden among the disorderly branches of the pear tree.
She stood behind the counter, neatly compact, with smooth night-black hair and skin like unbleached silk.
Or you can bring up the skin color as a way to say something useful about the character. Skin color as identification.
As in:
He spoke with a Gascon accent. He looked Gascon also, black-haired and slim, with the smooth, dark skin of the south of France.