When painting photorealism it’s very important to get the colors right.
Here is a trick how you can come very close the colors on you ref-photo.
1. Start by cutting small holes in the reference-photo. Be careful not to cut in the canvas.
2. Mix a color you think could work. Spray (if you are using the airbrush) it on a piece of paper with holes.
Hold it against the photo to compare the colors. In this case my color was too warm so I have to adjust it.
3. I added a drop of blue-violet to my mixed color, spray and compare again and now I am pretty close.
4. When I have painted on the canvas I can check the colors again using the holes in the photo.