There is one way with Morague's overlay, if you have the time and patience to learn how it is done......
http://www.modthesims.info/download.php?t=239851It works the same way as the game overlays(burnt/electrified/Tanned/plantsim etc)
But making a new package is difficult(even with the tutorial)
If this is for private use you better download a tattoo overlay and edit it to your liking and add some sock textures.
But keep in mind this overlay is not a accesoire and will always stay on(even in the shower

)
Other then that it is not possible.....offcourse you can make a new mesh but it is wanted in the accesoires category so you end up with 2 meshes ingame(clothing and accesoire)
Socks are normally textured on bottoms or fullbodyoutfits and those can not appear as accesoires as they lose their skintone.
Hope this satisfies your questions.