A useful tool!

When plein air painting or painting in the studio and I am struggling with, "what is that color?"  I use a 3" X 4" Index card that i have used my hole punch on.

AFter I mix some paint that I think might work, I put a small amount of paint next to one of the wholes and is using a photo I put the whole over the color I want.

And then I can adjust the color and or value.  This eliminates what I "think" the color should be!

Here is another example:

The card can be used several times and when one side is used up, let it dry, and use the other side.  This simple method is useful when plein air painting.  Instead one looks thru the hole to determine the color of the object that is being painted.