We have a lot more information about Roman wines than Greek wines. We also know more about wine-growing than about the wine itself. Theophrastos On plants 1.12.1 states that black mulberry and myrtle both taste like wine, which gives some indication of the taste desired: for reference, black mulberry is both sweet and tart, and myrtle is sweet with some bitterness and tannin. In poetry, the colour was usually said to be melas, a term that ranged from black to the colour of blood to the colour of soil. I'm not aware of any percentages, I'm afraid.

We can at least be sure that wine-growing was sophisticated and done to a high standard. For the Archaic period, Homeric epic reports on a significant wine industry in Boiotia, Euboia, Lemnos, and Phrygia, and on a smaller scale in some other places; and Iliad 18.561-72 gives a portrayal of wine-growing (and makes it sound like something out of Disney's Fantasia). After that, we get more information on wine-growing in Xenophon (Oikonomikos 9.1-12; only at the end of the passage is it specified that the conversation has been about vines) and Theophrastos (On plants, passim; check the index s.v. ἄμπελος). But for the most detailed information we have to wait until the imperial period, in Pliny's Natural History (1st century CE). He's Roman and Italian, of course, but he certainly drew on Hellenistic technical literature for his knowledge: one papyrus, P.S.I. 6.624, comes from a handbook about the treatment of grapes, so such things certainly existed.

There were several prestigious wine-growing regions, including Thrace and Thasos, Lemnos, and Messenia. In the 5th century BCE the government of Thasos took great care to boost the status of its wines by putting Dionysos and bunches of grapes on their coins, and passing detailed laws controlling the growing and distribution of wine, apparently as a very early attempt at an appellation system. The New Pauly writes:

The great importance of viticulture in the Classical Period is suggested by the frequent mention in historiography of the destruction of vines in times of war, by the great deal of attention that Xenophon paid to viticulture (Xen. Oec. 19,1-12), and by the wide recognition of wine and its consumption in literary and philosophical texts.

From Theophrastos and Pliny we can also determine that ancient Greco-Roman wine growers were well aware of the importance of grape variety, soil, and climate. Theophrastos On plants 2.5.7:

Most important of all, one may say, is it to assign to each the suitable soil... There is the greatest difference, one may say, between the different kinds of vine: for they say that there are as many kinds of vine as there are of soil.

Another papyrus, P. Cairo Zen. I.59033, documents the Ptolemaic kings importing a number of Greek grape varieties into Egypt. The Oxford Classical Dictionary (3rd edition), focusing mostly on Pliny, reports:

Most of the modern methods of training and pruning vines were already known, from the free-standing bush, propped vines, to trellising, and most notably the growing of vines up trees. This last was such a distinctive feature of some of the most prized vineyards of Roman Italy (e.g. Caecuban and Falernian) that Pliny (Naturalis historia 17. 199) could claim that ‘classic wines can only be produced from vines grown on trees’. Cited yields varied enormously; but these depended on grape type and the density of planting.

In Pliny's time the most prestigious wine-growing regions for the Romans were in Latium and Campania. But the Greek world did provide competition: Aegean wines were competitive with prestigious Italian wines, even within Italy, and both went for higher prices than other appellations. Pliny tells us that some Aegean wine-makers cut the must with sea water to sharpen it. Athenaios 1.27d reports that the most important wine-making islands in the Aegean in his time were Kos, Chios, Thasos, Lesbos, and Rhodes. The other major wine-growing areas in the imperial world were in Syria and the west coast of Asia Minor. The OCD again:

Most of the prized wines were sweet whites. Characteristically they were aged for a considerable number of years, with a resultant darkening of colour as a result of madderization. This process of ageing was often accelerated by exposing the wine to heat by storing it in lofts above hearths. While it was accepted that wine ideally should be unadulterated, the long lists of additives in Pliny and Columella suggest that producers were frequently forced to disguise a deteriorating product.