The robot on the poster looks ready to spread some joy, its arms stretched out in an embrace and holding hands with a plant. The robot's eyes are wide and its mouth is small, suggesting it is feeling content. Its round, bulky body is a friendly colour, and it looks like it is genuinely happy. I would suggest bright and cheerful colours for this scene. Use light blues, greens, and purples to colour the robot and the plant, and give it a background of optimistic yellow and orange. These fresh colours will make the scene stand out and will bring a sense of hope and joy to it.