Well, I have this idea of creating a tank top that is actually 3d, and not where the clothing stick to the skin. The image showed what i have so far. Problem is there is this patch of shadow between the breasts. I had certainly smooth the shirt already, but the black patch is still there. Anybody can offer solution?

Also, the polygons sometimes disappear into the skin when the sim make different pose. This is probably the bone assignment right?

If you are trying to build that 'shirt' as a second layer and lay it over your body, I can tell you right now that it won't animate right - at various points as the sim moves and bends, part of the sim body below will show through. That is why if you look at maxis skirts, there are no legs inside the skirts, even legs a good distance from the outer skirt will come through as the sim moves. It has to do with how the skeleton animates the vertices around it.

Even when you make the bone assignments match exactly the bone assignments below, if the shirt is away from the skin at all, you will have this problem. I just spent most of two weeks working on this exact issue with a skirt.
The way to make the tank top 3-D would be to modify the base body mesh to have more points to it, and then carefully reshape it to have a little bit of an edge.

Btw, while it's an interesting idea, I personally prefer my meshes without built in 3D necklines, because then that's the only neckline design that can be used, which is kinda limiting.

I think it may be possible as long as you stay away from th major points of movementlike the legs and arms even though you may have to make it a little larger than you want.It also may drive you crazy makeing the bone assignments.

As far as the shadows what method(tools) are you useing I may have a few suggestions.

I'm using unimesh, and i normalise by deleting away the body and smooth all and importing the cloth again.

If you can use smooth with unimesh now with no problem the delete the problem faces one at the time and then create new ones.Don't delete the verts or you will have to start over with joint assignments for those.

Then smooth, you may need to invert a face or two if they end up faceing the wrong way.You will also have to make a new uvmap for the new faces.

Hold on. You cannot should not ever ever do smooth all in unimesh while editing a body. It will ruin all of the maxis normals - and touching them up with the 'normals fixer' is still not as good as the originals.

You can save out the new parts of your mesh to a *new file*
(do this carefully, make sure you save your original work safely!)
Edit them separately (smooth if you need)
Save the fixed parts - in addition to milkshape format, export it as obj (if it didn't have bone assignments or you want to redo the assignment), or export as a gmdc if you want to preserve the bone assignments.
Open your original mesh file.
Delete the section you want to replace.
Import the fixed parts.

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I will repeat this - do not simply 'smooth all' if working on a body mesh in unimesh.

Even if you hide the other groups of your mesh - 'smooth all' will do them all (this is unlike many of the other milkshape commands, but that is what it does). So suddenly every seam on your sim's body will become more visible, because milkshape's smooth is not the same as the smoothing that was originally done.

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What *was* 'fixed' with the newer version of Milkshape was regrouping, you can now regroup safely -- well, relatively safely - you must keep track of the original name of the group and you must copy the comments from the original group to your new group. But all the bone assignments are preserved, which was not originally the case.

A couple of suggestions - first, one of the Maxis swimsuit meshes has a top with a "look down the cleavage" effect, that might be a good starting point.

If you really do want a complete "overlay" sort of top, I would start with a skintight/nude sort of top, then select all the faces in the area where you want the top to be.

Do a "duplicate selection", and you now have the basics of the top mesh - just scale the size up a bit and you have a perfect overlay, all the vertices will correspond exactly with those beneath it and have exactly the same assignments so there will be no "bleeding through" when the Sim moves, and no issues with normals or texture-mapping. Just reshape this top as you like.

UniMesh is now updated so you can import a second GMDC file with all assignments included so there is no need to use the .obj format any longer, if you do want to use "smooth-all" on your new part you can delete the rest of the mesh, smooth all, then export it as a GMDC and re-import it again later with no re-assignment nightmares.