Value: Value is simply how light or dark a color is. I could say, "That shadow is darker in value", or "the snow is a light value." You may refer to the values in a painting as being correct - meaning that the artist has properly painted the lights, darks, and mid tones. You can never get a color right, unless it is correct in value. The red can never be the exact red you are going for unless it is the same value (lightness or darkness) as the red in your subject.
In the above rose painting, we can say that the leaves for the most part are lighter in value than the darkest background values. You may be able to see this clearer by squinting at the painting. The magic squint as Richard Schmid calls it simplifies the values for us so we aren't overwhelmed with all the value changes that are really there.
The lower part of the stem (lower right) is a darker value than the surrounding background.
What other observations can you make on this painting regarding value?