Hi! I think the drawing has pretty good color base, values are ok for the most part. It just needs a bit more color variation, saturation and a few highlights to make things pop. For flat feeling: try to think in 3D. Arm is not a rectangle, it is a cylinder; the shading on upper side of her chest suggests that it has volume so it should be treated accordingly. Lines should wrap around the form (e.g. clothing around her body, hand around the cup). Gravity is also something to be considered - since she is in a stationary position, the cloth should be oulled down by gravity. I haven't adjusted her left hand since I wasn't sure what you were going for. Hope it helps.