Every body part of your avatar can have a different skin color.
To find the avatar skin tab, go to Account
>Skin
.
To edit the skin color of the whole avatar, simple change the color next to Body Parts
, as shown below.
And press Save >>
Next to each body part there is a color selector that you can change.
Once you have selected the color that you want, press Save >>
Next to each body part there is a visibility checkbox.
Unchecking those will make the unchecked body parts invisible.
For example: