There are lots of ways to classify wine but one of the basics is by color, red, white, and pinkish or “Rose”. Contrary to popular thought, the basic color of a wine does not come from the color of the grape juice it is made from. It comes from the skin of the grape. Most grape juice used in making wine does not have much color.
When making red wine, the grape skin is left with the juice for anywhere from several hours to several days. The chemicals that color the skin dissolve in the juice along with other chemicals that add flavors. The most important of the flavors is tannin. Tannin is a flavor that comes from tannic acid. If you have ever drank a cup of strong tea and had a sensation that makes your mouth pucker and your tongue feel dry, that is from tannin.
Tannin is good in red wine for a few reasons. It acts as a natural preservative. This is important in red wines because they are generally aged for longer than white wines or roses. Also, red wines are usually made at warmer temperatures than other wines. Oxidation happens more quickly at warm temperatures but tannin helps prevent it. Tannin can provide a balance against the fruitiness of red wines. Also, that drying sensation I mentioned can make you want to drink more; making you and wine makers both happy.
When making white wine, the grape skin and juice are separated as quickly as possible. The color of the wine is pretty much the color of the juice. White wine is usually made at lower temperatures than red and aged for less time. The preservative power of tannin is less important; though white wines that have gone bad from oxidation are much more common than red.
Rose is a bit more complicated. The most common, and generally best regarded, way to make rose is to leave the grape juice and skin in contact for a short period of time, say a few hours. This gives some color and flavor but not much tannin. After that it is made like a white wine.
Some inexpensive Rose may be made from blending red wine and white wine. I have read about it but must say I have never tasted one made that way. There is also an exception to the statement at the beginning that a wines color comes from the skin, not the juice. Rarely, some rose is made from naturally colored juice.