Marc,
I know exactly what you mean. The funny thing about it is, the colors that tend to be the most transparent are sometimes the darkest! Sap green, paynes gray and my blue (forget exactly which one) are all very translucent when used straight out of the tube. I find that there are a couple of ways to help your coverage with these paints. First of all a little bit of white will put an amazing amount of opacity into any color. I know you can't always mix white in, but for your midtones and highlights it helps allot. I also tend to mix my shadow tones with some raw umber or even black in them. One, to cut the pure tube color, and two, it also helps in the coverage/opacity. Besides, you dont want most figures to look fresh and new, they almost all can benifit from a bit of "weathering" and the other colors mixed with your base colors help provide a bit of fading, discoloring, "used look" etc.
Now one thing to consider, if you undercoat your surfaces in a base coat, say some sort of acrylics, use a much darker shade than you think you need. I am just now figuring out that on red for instance, if I go almost 2 or 3 shades darker in my base coat color, it helps tremendously in the coverage of my red oils because red tends to be very pesky when it comes to coverage. The midtones and highlights that are mixed with the lighter colors (white, ochre etc.) have no problems at all covering the darker base coat. One other thing to consider, oils are layed on soooooo thin, that you may actually have to go back and re-cover your areas a couple times before you have what you consider a good transition of shadows to highlights. I find myself often painting an area at least twice, to get the contrast I want. It's certainly not rocket science, and I learn something every time I wet a brush!!!! I have only been doing this about as long as you have, it's one long, fun learning experience! :lol: HTH,
Jay H.
OKC