1. Open the folder where you have installed your game: I mean the PROGRAM folder, not the Documents!
   
   
2. Browse to: EA Games\The Sims 2\TSData\Res\Catalog\Skins
   
   
3. If you see a small file named Skins.package, with size 1Kb only, delete it.
   
   
4. RENAME the file Skins.disabledpackage to Skins.package.
   (If you DON'T see the .disabledpackage file or the Skins.package is NOT only 1Kb, then this solution is NOT for you: don't delete anything!)
   

That's all. All the crashes in the CAS, or changing appearance, or entering the lots should immediately stop; the unexpected hair colour or skin tones over your sims should also revert to normal.

NOTE: if you HAVE SAVED a lot while the sims were showing unexpected hair or skin colour, I'm not 100% sure that the hair or the skin in that lot will automatically revert to the right tones.


So, who was to blame for all this fuss? ME, and only me, I'm sorry.
The ability to rename the Skins.package was a discontinued function of the AGS that I forgot to remove from the final release.

Therefore, the problems were not due to a bug in the game or in some custom content, but only to a bug in my brain -

HOWEVER, this bug only affected the ANYGAMESTARTER: the BaseGameStarter never had this function, and doesn't rename the Skins.package.

I'm going to restore the BGS, and I'll soon post an updated version of the AGS (hoping that you'll still trust it )