I would use a light gray to color the rabbit's fur, creating some depth and texture. I would use a pink or red to color his pocket watch, as well as a yellow to brighten his waistcoat. The top hat could get a dark black or gray to stand out against the soft colors. For the roses, I would use a bright ruby red and a few different shades of oranges and pinks to give the flowers texture. The ground could be colored a bright green, while the sky should be a light blue. The clouds could be colored white and light gray to keep them looking fluffy.