The texture. Working off an old Peggy mesh I've used for some recolors previously, and the buggy scalps for the younger ages always bothered me. Plus, the original hair is way too long for my use, so I shortened down the alpha (I still want the originals the way they are, so the mesh stays roughly the same). I'm also working on fixing and making some other meshes where editing the alpha may be an issue if the hairs don't have a proper scalp.

I've seen a lot of shortened (by texture) hair recolors from older hairs, and they often end up not looking good because of a missing scalp, so it's often a good idea to have a full head back there.

Resource files (for me and other lazy people who can't be bothered to extract the base files every time)
I made some starting meshes for myself a few months back, and extracted all the bases, added the faces and scalps with proper bone assignments and comments - might save some work for people. Wouldn't recommend using the Milkshape files for clothes (you should always start fresh), but they've got working scalps for hairs, and accessory resources (frame/lens with proper comments for copy/pasta). Just in case, all the extracted GMDC and OBJ files are there (the face GMDCs don't work very well to import). Make sure to remove the unneeded mesh parts before exporting, though. Everything is sorted by age via filenames.

Extracted resources and basefiles: https://www.simfileshare.net/download/938754/
(there are GMDC/SimPE files for the hair+face, if you want it with bone assignments for testing with clothes or some such. They're the "--head" files, and have proper bone assignments without causing morph issues with the face).

PS: Don't use them for animations (they're not made for that since they still have the hair bones active - I've got fixed files for animations right here in case anyone wants them, with hair bones deactivated).