This is the way it goes. Mix the paints I’ll use on my glass palette and transfer the paints to the old school beechwood palette that can be held while painting. I laminated the photo so I can mix a color I need then actually paint a very small spot on the laminated photo to see if I got it close enough. I also have a “color checker” that a friend made for me a while ago. You mix the paint and put a little bit on the tip of the color checker. Then “aim” the color checker at the color on the photo you are trying to duplicate and see if the color on the tip of the color checker matches the color on the photo.
