If you need to pick a colour to match, you need to isolate it from the distracting surrounding colours. There are many ways to do it. Many just cut a triangle out of some paper stock. A whole punch is faster and easier.
Hole punch and some card stock. You want it a bit heavier then paper so that the image does not show through the paper.
That is as far in the punch can reach. So I made one in each corner.
Ready to select which colour I need to pick.
Pretty close after the 4th try.