Normalizing Human Skin Colors for User Interaction
olayforyou.com defines these skin tones
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- very fair
- fair
- olive
- dark
- very dark
Any person using cosmetics regularly would understand these terms. These rest of us are just guessing :-)
I'd do something like the Nintendo Wii's Mii Editor and just show several swatches of colors. Even if the monitor isn't calibrated, if someone sees them all on the screen at once they should be able to make the correct choice.
You can then give the color an internal name and do your data mining on that.
You may wish to consider skin tones defined by cosmetic companies as these can be quite exact and even refer to tanning effects.