@Artichoke Lover I love a good green grape too. We have fabulous South African grapes in the stores here. They are so, so delicious! There are a few excellent South African varieties we get here actually; one of them has the faintest flavour of
roses 
. I planted a 'Somerset' grape a few years ago, and it is one of those rare table grapes that will grow well in my climate. The 1st year it made 3 large bunches. It's greenish pink, and quite small, but the taste is out of this world & wonderfully sweet. I find the dark wild purple ones tasty, but you can only eat so many because they are just too sour.
More pertinent to your question though, green skin in grapes is a mutation in that they don't produce anthocyanin like red grapes. I'm not 100% sure, but I think as a result of that red grapes have higher rate of production than greens. Maybe too, because of that mutation the green grapes might be a bit trickier to grow.