How to protect a red wine's color

The juice of many "modern varieties" of grapes (hybrids), and the juice of some vinifera grapes can have extremely deep and vivid purple coloration--glass-staining purple in fact,which is kinda cool. But during the winemaking process, sometimes the color fades to cherry red or even a pinkish rose. What happens?

First, this information is provided by my friend Alex Fullerton, a winemaker:

Anthocyanins (the main pigment in red wine, red cabbage, blueberries, and many other things) are responsible for both the blue color in the grapes' skins and the purple color of the wine. Anthocyanins have a double bond that is formed at one of two different locations of the molecule depending on which location is more favorable, resulting in the molecule having two very different shapes it can take. In high pH it is more favorable for most of the molecules to twist one way resulting in blue hues, while in low pH it is more favorable for most of the molecules to twist the other way resulting in red/pink hues. 

The skins on the Monastrell grape, for example, are alkaline, resulting in a blue color while the wine is more acidic (but not extremely acidic, maybe around pH 3.8) causing a purple color (roughly half of the pigment is blue and the other half is red, red + blue = purple). A very acidic Burgundy, on the other hand, with a pH under 3.5 will appear very red.

And, from Wiki:

Anthocyanins (from the Greek words for "flower" and "blue") can appear red, purple, or blue, depending upon the pH. In flowers and fruits, anthocyanins make the color red, blue, or purple, in order to attract pollinating insects (in the case of flowers) or predators (in the case of fruits, which need predators to eat and then disperse the seeds in the fruit).

OK. but why do some wines see their color fade during winemaking?

This is from an Iowa State article:

In young red wines, the bright red (with purple tint) color is due to monomeric anthocyan pigments which are extracted from the skin during fermentation. During maturation, these pigments are progressively replaced by the polymeric form, which results from the combination of anthocyanin pigments with tannin. Monomeric anthocyanins occur in various forms, such as the red colored flavylium cation, quinoidal base (blue), carbinol pseudo-base (colorless), chalcone (nearly colorless), and as a bisulfite addition compound (colorless). The various forms of anthocyanins are present in equlibrium, which is influenced by pH and other factors. An important point to note is that monomeric anthocyanins are susceptible to bleaching by S02 and with a lowering of pH, the equilibrium shifts from the colorless to colored form.
During maturation, the wine is exposed to air. Oxygen (from air) plays an important role in the condensation reaction between anthocyanins and tannins, which results in the gradual loss of free anthocyanins and the formation of stable polymeric (anthocyanin tannin) pigments. It has been observed that the poiymeric pigments account for 50% of the color density in one-year-old wine. As the wine matures and more polymeric pigments are formed, the color shifts from red to orange and brick red.

The condensation reaction between anthocyanins and tannins is accelerated by oxidation. If condensation continues (due to oxidation), precipitation of coloring matter occurs.

The condensation reaction mechanism includes participation of acetaldehyde under aerobic conditions. The polymerization of pigments also occurs in the absence of air. Oxygen is not involved in this reaction. In the absence of acetaldehyde, copigmentation between anthocyanin and d-catechin has been noted by many researchers.

Summary of all that: So, adding too much SO2 (sulfite) bleaches wine color. pH also plays a role in color (higher pH leads to blue/purple color; low pH leads to red color). When anthocyanin combines with tannin, that reduces color intensity. Oxygenation spurs the process of anthocyanin-tannin combination, which degrades color, but that color loss can occur without oxygen. I note that many winemakers work to limit oxygen exposure during and after primary fermentation; color protection may be one goal of such a practice.

Second, winemakers can add color concentrates to the wine, to darken and enrich its color. Such products (made from richly-tinted grapes) are expensive, and past a threshold they impart objetionable aromas/flavors, and they raise the sugar level too high.

Another method, common in the vinification of Syrah, is to add 5% or so of white grapes to the red grapes during fermentation. It is not intuitively obvious, but this helps to fix the deeper color. (It is also done to improve the Syrah's bouquet.) 

Biochemists continue to try to unlock the winegrape's color mysteries; I am sorry that I cannot find more useful information at this time, but perhaps the above info will be helpful . . .