This is an image of a "View Catcher" from Dick Blick at http://www.dickblick.com/products/viewcatcher/. This year, I learned to use the holes that, on mine, are both on the slide and in the corner of the frame. Looking at an isolated area of a lit setup through these holes, framed by the midvalue grey, allows for an accurate assessment of the color of an area of the still life object. For example, instead of "thinking" of the "red" of the apple, you are able to accurately see the "blue red" in the shadow, the "orange-red" in the light etc. You can also mix your paint and look through the hole and directly compare a knife loaded with your mixture to the piece of the object you are painting. Asking yourself then if your mixture is the correct value or intensity, you can correct your paint mixture, re compare and place the correct color onto your painting in the correct location. This means that you paint what you "see" not what you "think you see". Try it and see how much your paintings improve. You can make a "color isolator" by painting a midvalue grey onto a square piece of mat board and punching a central hole. The advantage of the View catcher, is that the slide also allows you to "frame" a scene. This will allow you to plan a composition or to create a more accurate block in or placement sketch.
This little painting of a "Plover from Sylvan Heights" was juried into the 2015 Women Painters of the Southeast National Exhibition. The show opens this spring and I will post details later.