Answer:
I would say value.
Step-by-step explanation:
You can have a piece of at that is completely devoid of what you would consider color, so it is completely black and white. The values are what make that piece. You can have shapes in a painting or piece of art without having the correct values. If your values are off, then the whole piece is off. Variety isn't even considered one of the 7 most important elements of art so that is out of the question. You can make a black and white painting but if the values are too similar, then it looks bad, so you need to have good values in order to tell they eye what it's seeing, what the shapes are, what the image is. The values describe the painting.