Color Sketch or Study
Here is a wonderful example of the difference in finish between a color sketch or study and a finished painting. This particular sketch is done in chalk pastel and the final painting in oil. Notice that the artist (Anne Kullaf) has set her palette and identified the largest blocks of color in the composition. There is particular attention to color temperature and its use to create depth and mass. You will also see that there have been subtle changes in proportion and scale but the palette remains fairly true to the original plan.
This process will make for less fumbling for color while working with your paints and allow you to focus more on your paint application and manipulation. Take the time to correctly prepare your color sketch and you will surely see a great improvement in your work and grade.