This sad looking cat is curled up into itself, its head resting in its paw. It appears to be quite stressed with its fur fluffed up to emphasize its size. Its dark fur and deep yellow eyes create an expression of dejection that is quite heartbreaking. To bring out this sadness, I would color the cat a shade of muted grey and done a yellow wash to tint the fur and bring out the eyes. I would use darker tones at the top of the head and then blend it out to a more pastel shade at the bottom. The paw should also be shaded to bring out its shape and emphasize the feeling of exhaustion. Finally, I would use a darker grey to color in the eyes, creating a feeling of sadness and despair.