Why are some wines white, some red, and some pink?

White wines are generally made from grapes with yellow or green skins. White wines also can be made from black-skinned grapes if the juice is separated from the skins prior to fermentation.
 
Red wines get their color from being fermented with the skins of dark grapes.
 
Rosés get their pink color as a result of limited contact with the skins of dark  grapes before fermentation. Rosés also result from mixing finished red wine with finished white wine.
 
Source(s):

Supermarketguru.com "Wine FAQs: Basic Wine Info"