Freezing any fruit before fermenting helps break the fruit down and release all of the goodies, color and flavor included, though it’s not the only way to encourage the extraction of these qualities. Many factors affect the color and color retention of wine, enzymes, more vigorous punch downs, good tannins to bind color, warmer fermentation temps to name a few.
As far as flavor, much depends upon the grapes themselves being good quality, different yeasts enhance different flavors, fermentation temps affect aroma and flavor, some yeasts produce more glycerin, which can enhance mouthfeel and the perception of fruitiness. Simply using frozen grapes won’t guarantee results, it’s a whole family of decisions that contribute.
You can buy frozen grape must (crushed, destemmed, then frozen in pails) from a number of sources, Brehm, GrapeMasters, Musto to name a few. Simply thaw the must and proceed as you would with any wine from grapes.