The color of the grape used.

Tannins from the skin of the grapes used to make red wine.

Do you mean component as in anthocyanins (which contribute to color along with others) or component as in bioflavonoids and saponins (anti-oxidants, reduce cholesterol, fight heart disease, etc) or any of the other complex compounds that are extracted by the maceration (steeping, the longer it goes, the more color/tannin the wine has) of skins with juice? The point is that there are many components of both white and red wine but the big difference is in specific production techniques that are applied to white or red wine. As others have mentioned, the skins of the red grapes lend color and a whole host of other components to red wine that are not found in white, which is why red wine is particularly singled out by research into the anti-oxidant and cholesterol lowering properties of wine (all that stuff in primarily in the skin of the grape). Honestly, if you read some of the conclusions of these studies (even filtered through the media) you'll notice that most of those components are also available through grape juice and fresh grapes. You can consume more of those if you're trying to realize some health benefit. I think, wine is a relatively poor choice as a drug, but I think very highly of it as a pleasant, relaxing beverage to accompany a meal or celebration (even if you're only celebrating wednesday). Cheers