Hydrangea: The background can be blurred a bit so the flowers & leaves stand out with sharper edges.  One idea of the Principle of Gradation is that a color change could occur in every inch of the canvas/paper.  This can be done by changing the Elements of Value (light moving towards darker), Hue (red moving towards purple) or Intensity (bright moving towards dull)__ or vice versa__ of the colors within each inch, or a combination of two or all three.  This prevents boredom/dullness by making sure each petal and each leaf differ from each other.