The use of cool colors in an artwork typically highlights the principle of "color harmony" or "contrast," depending on the context of the piece. Color harmony refers to the pleasing arrangement of colors, which can evoke a certain mood or feeling in the viewer. If the cool colors are used in juxtaposition with warm colors, this can create a strong contrast, making the principle of "contrast" more evident.
If you have specific details about the image in question, such as its composition, subject matter, or other design elements, I can provide a more tailored response regarding the principles of design being utilized.