Graphing color can help you identify colors more specifically and understand relationships between color better. One way to graph color is to use the Color Sampler Tool in Photoshop in combination with the Apple color picker.
To access the Apple color picker choose Photoshop: General Preferences and change Color Picker from Adobe to Apple and click OK. To see the new the color picker click on Set Foreground Color or Set Background Color icon in the Tool bar.
Unlike the Adobe color picker, the Apple color picker is a color wheel. Creating and using color wheels to describe color and plot color relationships is a time honored tradition dating back to Leonardo DaVinci. Some of the most famous color wheels were created by Newton, Goethe, and Munsell. The Apple color picker is an additive color wheel where complements are defined as red and cyan, green and magenta, and blue and yellow.
You can sample any color in an image and find its position on the Apple color wheel. Using the Eyedropper Tool, sample a color in a composition. Then click on the Set Foreground Color icon. The Apple color wheel will appear and a small circle will plot the sampled color. You can make a record of this chart by taking a screenshot of the color wheel (caps lock, Shift, Command, 4). This will create a PDF document on your desktop, which can be opened in Photoshop.
You can combine multiple sample points into a single chart by taking multiple screenshots, opening them in Photoshop, and combining them. Drag the Background layer from one document into another and give it a meaningful title. Make sure the two layers are registered with one another. Then, mask off everything on the top layer except the circle identifying the color on the color wheel, the triangle identifying it’s luminosity on the slider to the right of the color wheel, and a portion of the color bar above the color wheel. You’ve just graphed the two colors on the Apple color wheel. You can do this with as many colors as you desire.
Once colors have been graphed you will be able to identify a variety of relationships between colors, both colors that exist in a composition and colors that do not.