Today, I was just researching something I heard on David Laffel's video about painting the translucent objects not by painting their color but by painting the "transmitted light" on the other side of the grape. Robert Liberace just mentioned a similar principle about painting the iris of the eye in class the other day. (At least I think it's the same/similar principle). Rob explained that we can see the color of the Iris best on the opposite side of the highlight. (You know that little round dot of light that often reflects off a model's eye because we set them up in a spot and the shape of the light is round with a flash of color on the iris - that's the one I'm referring to).
Well, I'm teaching students to draw and paint glass right now ... So, here is a painting that illustrates this point. The paintings by Carol Thompson of grapes with the lemons below (or grapes and peaches above) emphasize the color of the light on the right (from the viewer's perspective) side of each grape and the highlight on the left.