Appearance

NOTE: See Appearance Editor for more recent information.
This page is part of the Second Life User's Manual, describing how the Viewer software works. Please see the main User's Manual page as a starting point.
The "Appearance" floating window allows you to edit how your avatar body looks. It is activated by the top menu Edit > Appearance... item, or by pointing at your avatar in the 3D view area, right-click for context menu, and choosing Appearance. When you open the window, your avatar will go into "Appearance Mode", and will stand with arms and legs spread for visibility, and the camera will zoom to view the relevant part you are editing. You can move the camera view while in appearance mode to see how you look from other angles.
There are four body parts and nine clothes tabs, each with individual controls. These all affect your core avatar body. In addition to these, you can "Attach" up to thirty 3D objects to different parts of your avatar. For example, a backpack, hat, and walking stick if you want to look like a mountain hiker. Between the Appearance settings and attachments, you have great flexibility in what you look like.
Each tab will list the inventory item name and location that you are currently using. If you are wearing the item, you will have a button to take the item off. If you are not wearing the item, you have a button to create a new one. At the bottom of each pane are buttons to Save, Save As..., and Revert. Revert will undo all changes since the last save.
Adjustments in appearance mode will show on the screen immediately, but will not be saved until you use the Save or Save As... buttons. It's a good idea to first make a copy of your current appearance in your inventory before editing it. That way if it gets messed up, you can go back to the original and try again.
While clothes can be removed, the four basic body parts (Shape, Skin, Hair, and Eyes) cannot. They can only be exchanged for another inventory item of the same type, or edited.
==== Shape Tab ====
Your avatar's shape is defined by a 3D wireframe model, as illustrated here. It consists of numerous triangles, on which the skin and clothes are painted by your graphics card. The shape tab adjusts the wireframe model using sliders or number values to change detailed parts. The entire collection of settings can be saved as an inventory item. When you "wear" the saved shape, it will adjust all the settings at once. You can create your own shape from scratch, or get pre-made shapes from other users or buying them.
There are 9 buttons to control different parts of the shape. Each button displays a set of images, sliders, and number values from 0 to 100. The images show what the extreme (0 and 100) values would do to your avatar's appearance, and the sliders and numbers show your current settings. There are 77 shape controls in all, grouped as follows: Body-3, Head-11, Eyes-11, Ears-4, Nose-10, Mouth-9, Chin-9, Torso-12, Legs-8.
==== Skin Tab ====
Your avatar's skin consists of three images (head, upper and lower body) which are mapped onto the underlying wireframe shape by your PC graphics. There are also several controls to adjust color, freckles, and other features. 
The three flat images are "wrapped around" the 3D shape, being stretched as needed to fit. Since the wireframe shape can be stretched and distorted in many ways by the appearance controls, a particular skin may look better on a particular shape. In addition, the lighting in Second Life varies during the virtual day, and local and portable lights can also change the lighting. Thus any shading or lack of shading in the skin texture can be affected by the lighting conditions.
If you wish to understand how to make your own skins there are templates available which show what parts of the images end up where on the avatar. Skin textures will be forced to 512x512 pixel size for sending to your Viewer program, so it is best to create them in that size in the first place.
Depending on the transparency or lack thereof of the skin images, and the edit permissions provided by the creator, the adjustment buttons and controls may or may not be available or make any difference.
==== Hair Tab ====
When Second Life was first developed, the avatar model included a second wireframe mesh for the hair. This is known as "mesh", or "built in" hair. As of 2009, the default starter avatars and most experienced users use "attached" or "prim" hair (called such since it is made of prims - primitive geometric shapes that everying in SL is built from). These can be much more detailed - 100 or more pieces rather than one mesh shape; and can use the flex feature to move as the avatar moves around.
The mesh hair is still included as part of the avatar model, but most users have their settings set to "Bald", which shrinks the mesh hair inside the skull where it is hidden. Occasionally the mesh hair is useful if the prim hair has holes or bald spots. In this case it is made relatively short to work as a filler, and color matched to the overlying hair.
A single texture is stretched over the wireframe mesh to provide the coloring for the hair. Most mesh hair is editable, and there are buttons and controls to adjust color, style, eyebrows, and facial features. The hair color is additive to the color in the texture image (you cannot make it lighter than the starting texture).
==== Eyes Tab ====
Your avatar eyes are defined as a single texture (image) which is mapped to both eyeballs, and two controls to adjust color and lightness. Eyelashes are part of the skin adjustments, and if 3D lashes are desired, they must be worn as an attachment.
Second Life currently does not allow for each eye to be different using the appearance mode. Wearing a prim eyeball on one eye is way to achieve that effect.
==== Clothes Tabs ====
There are 9 clothes tabs for different clothing items. The first 8 are layered onto the avatar shape, following it's contours except for sleeve and pants cuffs. The last one (skirt) bells out away from the body shape. Each clothing item resides in one of three 'layers' which determines which is visible over the others and the skin. If the item can be edited, you can select a clothing "texture", and color tint, and use the sliders and number entries to adjust length of sleeves and hems, necklines, etc.
The clothing textures are flat images which are 'mapped' (wrapped around) your avatar shape. If you want to create your own clothing, you should get a set of "templates" which show what part of the image ends up where on the body shape. A full set can be found at Robin Wood's site 
Many clothing outfits consist of several of these clothing items, plus some 3D objects which are attached. While these tabs can be used to make adjustments to individual parts, to wear an entire outfit the easiest method is to select an Inventory folder holding all the parts, and Right click for context menu > Add to outfit. This will put on all the pieces, replacing any items which use the same appearance tab or attachment point. You can also drag the folder onto your avatar body.
When you log in, or change clothes, the Viewer program on your computer produces a composite image using the textures for the skin and clothing layers. This is called 'baking' your textures. This composite is sent to the server, and then to other users to see.